Having just gotten back into Civ 5 with G&K and new patch, I'm getting used to selling buildings now and realized something: Broadcast Towers arrive in Modern Era with Radio, and CN Tower comes in the Information Era, so it makes sense to build Broadcast Towers well before the CN Tower comes along. However, the turn before the CN Tower is complete, you can sell all your Broadcast Towers and gain 125 gold for each one, then get them all back for free with the CN Tower. Marvelous! I also realized I don't need to keep my barracks in all of my cities after I complete my Heroic Epic in my capital. If I'm not going for Science Victory or Time victory, just domination, I can also sell my science buildings once I tech out. There's no real point to having most of them if all they're doing is contributing to Future Tech score but draining gold. Things to think about! Any more tips?