I haven't seen this covered, but I haven't read every post yet:

How about the option to collect info on a planet without sabotaging an improvement? There are plenty of real life examples of allies spying on each other in a "trust but verify" sort of relationship. Most of the time, I'm more interested in increasing my knowledge of a civilization, rather than sabotaging them.

And if info gathering becomes an option, it'd be nice if the computer (and player) didn't have to take it as an act of war. An uneasy truce between civs might include allowing a spy to check up on what the other civ is up to.