I like this idea a lot actually, more so then removing it all together. So something that looks like this:
Bombardment special attack blah blah blah, takes all of your ships and may be your only action. Does 10,000 damage to a grid space to be distributed among all units in the grid (kill one move to next) facilities take damage first. (Hey why couldnt troops take cover in the buildings and sewers and what not.) G-Space #X Destroyed: Grid space is converted into a "Wasteland" (-1 UCR and half move for infantry and vehicles). Do not figure UCR into this attack. (that should take care of 10,000pts not being enough)
Then, we could think about adding an interesting aspect with that, say any grid space that takes 3 bombardments in a single battle becomes uninhabitable, untraversable wasteland. Then you really could "kill" a planet if you so chose. Just think, you get all 3 of you imp people you really could pull a BDZ manuver. Not sure if thats a good idea, but ultimately the game is playing for a real end so, perhaps it could be fun. Adds a civilization type aspect to it I think.