I actually think for a game as old as NWN, the newer graphic cards don't do as well as some of the budget ones that I used to get years ago.
Eg: I remember being on a NVidia GT 240 years ago, only had about 256-512 mb of memory on it, but it ran perfectly.
Then years later, after getting a GTX 850+ (Currently on GTX Titan) - I started getting NVidia driver crashes and it looked like the newer graphic cards were having trouble with Open GL 3d graphics. I know it wasn't just me who had this issue, as there was numerous posts about it on NVidia forums about how graphic cards were unable to play the game with reasonable fps on their newish cards.
In the end, NVidia eventually incorporated some sort of fix into the driver to mitigate/resolve the issue for NWN players.
The fact remains however, that the people on older cards were unaffected by the issue and could play the game with no fps loss or mishap.
I guess it depends on what you really want to do with your graphics on nwn,
If you are wanting to get a huge resolution for nwn, that can fill a 4k screen - then yes, you will need a big graphics card (Several hundred $$$)
If however you just want stable fps and good game play - you could make do with a budget graphics card ($40-$60).