I think Spore desperately needs something similar to WorldEdit for Minecraft.
Making big and detailed adventures just takes a really long time.
I think it'd be insanely helpful if a mod that could speed this up was made.
I was thinking that it could reuse the selection box from the Tribal and Civ. stages, which is traditionally used for selecting multiple units at once. The adventure editor version would be able to select multiple creatures, buildings, vehicles, effects, etc. You can use this to rotate multiple props at once, move multiple props at once, delete multiple props, etc.
I think the most useful thing this selection box could be used for is copying -- if you were to click ALT while having multiple props selected, you'd be able to copy and paste multiple props at once. This could be used to really speed up the adventure making process.
This would just be the beginning. There could be other features that could be added, like the ability to filter what kinds of props your selection box will select.