Hey there is a setting that makes all 3d rendered units to icons, maybe it is not so difficult to let some parts be icons others not
there is no setting that allows you to rend ships as icons but not planets. there is no way to mod around this. Stardock AFAIK only has 2 staff members allocated to developing GC2 further at the moment. if you want to play the game for the strategy, it seems you'll have to give up 3D plaents. honestly, the textures are really low-res on planets anyway, and really aren't much to look at. if you want to enjoy the graphics, it seems you'll have to deal with the lag.
another thought occurs: what map settings are you playing with? if you're trying to play a max settings on a gigantic map on a laptop, you're being unrealistic. power-gaming PCs with the highest end equipment sitll experience lag on maxed-out maps.
lag isn't pleasent. but it's better than constant crashes. even with 1.6 and not playing max settings, i can get really low FPS at times.