Someone else mentioned this a while ago, and I'd like to bring it back up with a post of its own. I would really like the ability to obsolete buildings from my planetary lists. If I know how to build a 15% econ structure, and I trade for a tech that gives me an 8% structure from another series, I have to spend the entire game looking at the useless building and trying to find the better one. If I keep trading for all the passive bonus techs, I end up with about 20 useless buildings cluttering up my choices.