One last suggestion (sorry I know you want to wrap this up). Instead of a high price tag there should be a limit of how often you can build a new monument. Say once every in game year at a price of 100 gold or so. 500 is so high that I doubt anyone will bother to build anything.
There could also be varying prices, like 100 for a small plaque, 200 for a statue, 300 for a huge statue.
