Another reason to purchase the buildings I listed in my spreadsheet is that the upkeep is much better as well. While the smaller items which have an equal return on investment are only giving you 9S to clean them, the larger ones give much more. For example, a granary will give 90S and a Roman Gate 105S. This may not be the same as if you had purchased the same amount of Silver worth of the smaller ones, but again... less selling them back to make room for better ones, and higher impact per square the whole game.
Another thing I noticed today deals with embassies. If you needed any motivation to get mote allies this is it! = Cleaning an embassy will also yield 100S at level 1, but as you level up your embassies you will get increased silver for visiting AND cleaning them. This quickly becomes 150, 200+ per click, usually each day. If you hadn't noticed, as they level they also increase in Happiness as well.