The price inflation as far as cash purchase and upgrade is most likely due to the recycle glitch which caused many players to generate 100's of billions in just a couple hours before Gree could create and push the fix. Basically trying to level the playing field by getting these people to spend billions to upgrade these buildings at the top levels. As for the gold buildings that's just Gree trying to make more money. To be honest I hate giving my money to Gree(dy) but this is one circumstance I don't really mind.