I'm pondering replacing the LCD-3s with the TH900s for when I want a pair of cans that are more exciting compared to the 009s which are ultra-refined. The LCD-3s were my kick-in-the-pants cans, but they don't do enough of that. The other solution would be to get a big tube amp for them or wait for the closed LCD-2s. That would be a tough call then.
I think in the long run it will be a lot cheaper if you get the TH900s now