I am up to 5. I don't stock up in the double digits too often, but I think I will head towards 10 on this one. I think it is winner because Frank Lloyd Wright is a star of architectural design like Batman or Spiderman to comic book fans. This is a great model, and there are a lot of people that don't realize lego makes these models. As they see them, the early ones will be valuable like the first wave Batman sets. The Robie is the biggest to date, and is a sleeper because it isn't as well known as Fallingwater. I will continue to collect these if I can find them around $150. My TRU has them that cheap whenever there is BOGO sale.
It think it has a good chance to hit $400 within 2 years. It might not be a quick flip, but I wouldn't be surprised if it went a lot higher. There has never been a large architecture set retired. We will have to wait and see. It hasn't seen huge discounts and sold out pretty quickly from Amazon. We will have to see how many are in the TRU and Barnes and Noble systems. Not many other places have them around me. The entire Architecture line is still a sleeper with most people, even after its performance this holiday season.
Don't forget about Fallingwater. I pick these up below $75. I think it will have a higher CAGR than Robie House.