I add random enchantments the same way you show in your example.
I use Silicon Scout's treasure system to equip my mobs with random weapons, potions, ammo, scrolls or various other junk. My scripts then add random enchantments to the weapons and ammo.
I also have random armor and item loot that is enchanted the same way and some mobs may drop it or it might be found in loot caches.
Add in ShadoOoW's boost system for random stats and effects and Sir Elric's random traps and the mobs, areas and loot stay interesting for quite some time. My basic goblins are typically weak against something like Ghostly Visage because of the 5/+1 but then some goblins will start doing an energy damage type and another will have a +1AB or Enh weapon and whack you pretty good.
The enchantment scripts are long and a bit integrated into my module and its magic level but if you want to see them I could send you the erfs or post the code to copy.
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