I think we're beginning to stray abit of the OP, but ... in the OP (I'll paraphrase) it was stated that PCs need to be of "mid-level" to have an impact on a PW. Later, "Zwerk" (who's hak work I use alot and look forward to more of constantly) states that PCs need to get to at least 5th level to survive or thrive. While in general, I agree with both statements, I see them as stereotypes, but not absolutes.
Over the years, I've had the pleasure of playing with several folks that from the first time they logged in with their new PCs, they were making an impact. They had story lines/backgrounds full of detail and interest and best of all, shared their characters with the rest of the players while not being overly dramatic. I.e., it was enjoyable to get to know these PCs, therefore lots of PCs of all level ranges interacted with them and many times these low level PCs opinions/actions/etc did influence a PW. Of course, these were Role Play themed PWs as these same characters would have respawned endlessly in most other environments.
As for the "need to grind", well ... NWN is a computerized version of Dungeons and Dragons. In "DnD", the bulk of wealth and experience does come from adventuring, AKA "grinding". Its "Dungeons and Dragons" afterall, not "Wheelwrights and Seamstresses", not "Barflys and Farmers", not ... "Second Life" or "The SIMs". In DnD and by extension NWN, the goal is generally to get off that barstool, dust off your boots, refletch those arrows and head out to overcome obstacles and creatures and become ... Heroes or even Anti-Heroes. On my own PW, I do reward RP, but the bulk of wealth and experience for PCs is still found while out exploring.
"Zwerk" brought up some good points about survivability at low levels and I mostly agree. He also pointed out that many Modules/PWs lack a story or a reason behind the "whys" of many quests or dungeons. I agree mostly as well. As an Admin/Host/Builder/Scripter/Player II can also attest to the fact that it all takes time. Creating a quest, writing all the NPC dialouges, building the areas is often fun, but ... doing it over and over and over can fast be draining as you struggle to make each addition new and unique. 
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The "Dreaded Rats of Doom" and "Endless Lines of Zombies" are a given on most PWs ... unless PC simply level up several levels upon entering. Being an "old school" PnPer, I dislike modules where you start above 1st or 2nd level. I want a challenge, I want progression, but I want time to find my footing and get a feel for the environment as well. There's PWs where after joining at 1st level, you do a quest and when completed, voila!, you're 2nd level now. I always feel cheated by these. Why not just start me at 2nd to begin with, especially since the quests rarely help me learn of the PWs systems, nuances and various dynamics. Still, its not easy accomodating new PCs with "survivable" challenges.
I hate rats, not RL rats, those I'm indifferent to, but rather the Bioware Rats and Dire Rats prevelent in most starting dungeons/quests. Mainly, its their disease inflicting bites and razor sharp teeth that can decapitate squishy mages and monks in one hit that get frustrating. Admittedly, I do use "rats" in one of my own low level quest areas. They spawn reasonably based on the PC or Party's level(s) though. They also lack diseased maws, do only 1pt of damage (unless a crit of course) and are "undead skeletal rats" for something different. There's also a reason for exploring the area, to determine why its overrun with "dead rats". Successful exploration will reveal that the "exterminator" which killed the intial real rats was a devotee of Talona with a warped sense of revenge. Being stiffed for the erradication, they wrought revenge by turning the dead rats into undead.
Zombies, skeletons, goblins, etc... are also neccessary evils to create low level adventures. In my low level areas, the undead have slightly slower movement rates, so you can usually run away if you need to. They spawn fairly appropriately based on the level of the PC or Party. There's also generally a quest with an explanation as to why they exist. Still, not all builds are the same. some classes are always going to be harder to play, especially at lower levels and I'm not a fan of the "all classes should be equal at every level school" since my gaming roots hail back to late 70's PnP. Being an "old fart" and "old schooler", I also find inspiration in DnD versions from the original up thru 3.5 edition. Old school encounters with "Xvarts" (2nd edition and found in the Baldur's Gate game), my skeletals priests are actually "Hecuevas" and many other such details. Still, what to do for those that have finished the quests, but still need gold and experience to continue?
To help out starting PCs (and be useful to all if the continue), I have several foraging, mining, fishing, hunting and cooking systems inplace. Find some berries, save the right type and a certain NPC will reward you for them (she likes to make freash pies). Glean from a wheat field and fill a bushel for a greatful farmer. Do a "deliver and return" quest for a local merchant. Go retrieve a child's lost toy (OK, that one involves defeating some "blue meanies", AKA "xvarts"). Anyhow, successfully mining ore or minerals grants a small XP reward, finding fruit, berries, grains or herbs does as well. Many "edibles" also restore 1hp when consumed. Cooking meals by combining ingredients in a pot or stove creates "meals" that restore 4hp or more when consumed. Catch a fish and get ... XP and something to cook ... or just sell your catch for a couple gp. Locked or locked and trapped chests can be "bashed" and you'll just get a lesser loot reward, but pick the lock and get some XP rewarded and the same if you remove/recover the traps on doors or chests.
I think that what is more important than shear levelling speed is whether or not there is something to do that not you've not already done a half dozen or more times at your level and is challenging yet survivable and entertaining. So allowing players to start out at an advanced level can save on resources (fewer areas needed) initially. Myself, I'm pretty anal about efficiency and thusly have a module I can grow constantly. So area count and creature pallette counts are of little concern to me (or rather, not a factor in expansion) and I can add new adventuring areas that fill in level ranges as I see a need. Still, folks like to progress and do so noticeably. On my own PW (values vary by player/PC/time spent actively adventuring) I average around 1,000 xp per 2 hours spent exploring. Not at low levels, but from 1st thru 20+ so far. Now, I do have to challenge myself. My 16th level Ranger won't make 1,000 xp killing effortless goblins for a couple hours, nor should he. If however he travels and faces foes more attuned to his own challenge level, he'll progress consistantly.
Over the years I've played NWN online, I've visited countless PWs. Some I hated, some I merely disliked, but many I could tolerate and a few I eventually even enjoyed. The one common thread was that, not a single one ever met all of my own wants or needs ... that goes for my own PW currently. Not every rule or feature is a deal breaker for me. By exploring other PWs, I've also seen what I liked and disliked and generally built my own PW based on those experiences. As an example, I dislike modules where you can "plop and rest" freely, especially in dungeons and dangerous wilds. At the same time, I found resting timers too restrictive, especially when you invite a "caster" to adventure with your party, but they need to rest to memorize a better spell selection and the whole group now has to "stand around" waiting for the caster's rest timer to expire so they can choose new spells. Or only being able to create X number of potions/scrolls/wands due to a lengthy rest timer. So my own work around has been unlimited resting, but only in designated areas that allow resting like an inn room or a "safe" cave, campsite, etc... in the wilds. So now, since most "groups" form up in or near a town, any delays are minimal if a caster desires to reset spells.There's been lots of other things I've "changed" to meet my own preferences and I'm sure I'll continue making changes/additions as time and skills allow.
Lastly, even on RP PWs, I've met tons of players over the years that assumed they needed to be a certain level to affect a change there. It isn't always true. It might be considered the "norm", but ... we can all be exceptions. Its up to the Admins/DMs though to notice and react.
Good luck to any and all who decide to create their own PW. Just do it for your own enjoyment and be willing to share it with others. If you seek praise and high marks alone, you'll just be frustrated and heartbroken in the end.
