However, why not try and make the other aspects of Spring's work for us in terms of physics and transport?
Unit idea: Basically a multi-story, thin tower with pigeonholes that moves and can load units. The key would be that the units could actually fire out while being loaded, and take damage in turn. Since the thing would be scaled vertically, units would not get in each others' way when firing, and thereby allievate the lategame issues.
Think of a smaller-ish version of this on treads/wheels:

This way is more realistic *and* it helps avoid friendly fire issues.
Edit: and for those of you who say that this wouldnt be good because all units would travel at same speed - when you have a large mob of units and you click on the enemy base, arent they all just mashing into each other, slowing each other down, etc etc, anyway? The mob moves as a group in either way, so this wouldnt be changing things. Hell, if speed-changing is properly implemented via script, you could even have a unit that moves at the average speed of its transportees
