Are they worth it? I generally build them once I reach opera houses for two reasons: 1) They cost a lot in maintenance and are less efficient at giving culture than monuments. 2) Lots of early culture can be a bad thing. Let me explain this. Generally I'm going to fill out 1 of the first 3 trees (depending on strategy) and then either rationalism or freedom. As I never save policies, getting too much early culture would force me to pick sub optimal policies that will drive up the cost of later policies massively. Only occasionally when I go down Patronage/Piety is this not the case (I have yet to find a use for commerce). I very rarely find that I have to pop my borders fast, and will buy a tile when I really need to. 3) When I reach opera houses (more efficient at giving culture than temples) I am in the renaissance so lots of good policies are available. I generally go for rationalism + 1 of the last 3 trees so need lots of culture to get the juicy policies at this stage so build temples and then operas in quick succession. The only problem is the damn expensive cost of those operas. Am I plain silly for doing this?