I feel the same way. It's become evident in the architecture theme that unless the set has a short shelf life like Sungnyemun that most sets not based on US landmarks dont rise as fast here in the states. If they are more obscure, then it takes a lot longer to appreciate. Last years Brandenburg Gate, LTOP, and the Villa Sovoye are pretty much RRP after fees right now or just the typical "thanks for the 5.00". I can see sets like the Eiffel Tower do well, but i'd be hesitant on hoarding a lot of Louvre, Burj Khalifa, Venice, or Berlins (all of which should retire next year). I could have bought about 6 Trevi, but I only grabbed one and the reason is i'm sitting on quite a lot of VS's, Brandenburg Gates, UN and LTOPs that I dont want to get stuck with another turkey.
Basically, it seems Chicago sets are money (Farsworth house, sears tower, JH Center = $$$) New York sets do very well. DC sets seem to have some legs too. And of course any set designed by FLW has shown promise. I think the US Capitol set will be a great one to have when it retires... But anymore, I think the Eiffel Tower and the US Capitol Building are the two sets that i'd eye to stock up. The rest, i'd buy light.