Mhh. I can't think of a single "smooth" game where I did NOT run into happiness problems in the midgame after building all available happiness buildings. I think as long as the start is not horribly food starved you pretty much have to buy some happiness (Luxes or City States) or stagnate your empire. And being able to grow further is totally worth the gold imho. Although the fact that being unhappy give me an 11% Science penalty once I've opened Rationalism is surely something to take into consideration if I get my happiness from shaky sources.