Removing the population cap would be pretty pointless, what with there not being any population to cap.
Unlimited health, energy.
Unlimited grenades, Demolition Charges.
Adding deployment points (Only one at a time, though.)
Adding Ability points. (Adding exp becomes redundant with this, as you get two ability points per level, no other changes)
That's all I can think about right now.
[Edited by Weresmilodon, 2/16/2009 1:46:23 PM]
Have you played the beta? There IS a population cap (in skirmish only, however), so a removal of that would be sweet.
Also, your hit points and energy get increased by each level, so you're wrong in saying there are no other benefits to levelling as well
Addition of unlimited energy/requsition would be nice too.
Other than that, those options pretty much cover it.
[Edited by PeTTs0n, 2/16/2009 5:20:13 PM]