For those curious, i've found the following benefits to using Zeckenslack's GLIDE wrapper:
1) Higher-resolution textures. There is a registry hack for working around this in D3D though:
http://homepage.ntlworld.com/karajorma/FAQ/fs1-technical.html 2) Smoother background nebulae. The D3D version has nasty color banding.
3) Better stars and motion blur. In the D3D version, stars will disappear if you are flying straight without turning. This is probably because the star pixels are smaller than the 640x480 resolution can display.
In the GLIDE version, the stars are always visible and have a slightly softer look which increases their size enough to remain visible.
Furthermore, the motion blur from turning looks a little softer and better blended under GLIDE as well.
4) Anti-aliasing and anisotropic filtering works again! AA worked in FS1 D3D on my GeForce 6600 and earlier cards, but on my GeForce 9600 it causes massive graphical errors. Works happily with the GLIDE wrapper though.
5) 1280x960 resolution! In the GLIDE configuration, you can select "try high-res" in the FS1 profile. And it works! There is a little bit of visual garbage in the HUD, but it didn't bother me much, and FS1 running at 1280x960 with 16xAA and 16xAF looks smooooth!