I too use D3D to play EAW and I have not noticed any real difference visually between the D3D and Glide in playing the base game.
If you do use a Glide Wrapper to play EAW, the default planes are okay, but quite a few of the communities addon on planes have visual problems (holes or vanishing plane pieces) caused by Glide that are not there for the exact same addon D3D planes.
At one time back (before Dec 2007), Glide did give the ATI video card players their horizion fog, but ATI fixed this issue with their Dec 2007 video drivers (reinstalled horizion fog on old games), so Glide now has no positives over D3D in playing EAW.
The bottom line is use Glide to play RB3D (as I do), but use D3D to play EAW. The way you do that, is just put the Glide ".dll"s into your RB3D folder so it only effects RB3D, but no other game.