Community member Symphony has made a very well made entry concerning NWN skyboxes, their inherent issue, what the community has done with skyboxes, and his own personal experiences creating them.
Skyboxes were one of the first things I worked with in NWN. A lot of my inspiration for finding content to make comes from looking around in the game and noticing ugly colors, noticeable pixelation, or poor performance. The skyboxes had all of these things for me.
Very interesting read, well worth your time.
You can read his entire post HERE