I noticed in the beta that upgrading from adv trade centers to banking centers seems to take a ridiculously large time. It seems more worthwhile to build multiple trade centers, but once you have researched banking centers I can't figure out how to go back and build trade centers. Does that mean I have to hold off researching banking centers on purpose, just so I can build a cheap (non 40-turn) economic bonus for my planets? It's almost like there are a few techs that I fear to get because they will completely stall my ability to build on empty planet spaces.