In balancing the UBs, since there is only one UB per nation, perhaps we should try to ensure that each UB has similar degree of general usefulness and could be created in a good number of your advanced cities. I.e. a UB for advanced general buildings like Custom House, Governor's Palace, or Citadel is a good choice, because those can be completed in a good variety of advanced cities and apply their special bonus. However it may be that Whale Oil Factory or Large Stable is built only in a few specialized cities and will have less overall effect, so maybe it's best to let their UB replace vanilla Customs House or Palace instead of those. I think Tavern and especially Market will get built a good amount, but they're also easier to build and have lower level, so perhaps their bonuses should be somewhat slighter than others, or alternatively that UB could have a somewhat higher yield cost to compensate.
