Eventually you will get to the point that you only want to keep what is ABSOLUTELY NECESSARY to function the way that you feel is best for your situation. e.i. For me I only have GBs, event buildings, and special buildings and building "sets" that are won through events or now the AD as well. I will only keep those event and special buildings that gives me the desired output. Which for me right now I'm focused on buildings that gives me happiness, FPs, attack/defense increases, and anything else is simply extra. I've removed everything else from my city. And I actually just went through and deleted about 12 to 15 SoKs. A few years ago they were essential to most players and were coveted. Now I feel that they only have that impact on newer players or newer cities. I still have like 12 or so SoKs, but I'm just about to remove them as well. I like to focus on upgrading all the special buildings to there highest levels and if it's a set of buildings that interact together, then I want to acquire all of them available and get the most out of them to get every possible reward for how ever many items they can give you depending on how you align them together. The only time that you will see a regular building of any kind in my city is say for instance I have a quest that calls for numerous productions to be made from production buildings and if that's the case and it doesn't have to be from your current age or age below, I will just build the blacksmiths to get that done then remove them afterwards. Unless, an event is in progress, then I may keep them until the end so I don't have to keep rebuilding them, since that is a quest that comes up often. Space is something that becomes so much more important as you go on, so if I was you I would definitely consider what you are looking for your city to eventually become and try to avoid building unnecessary or lesser buildings and trying to make them get you to that desired point, because it will take you so much longer to get there.