Same situation for me. I love my N900, but it is too slow for me and I miss some features.
I will stay with it until March/April and look at the prices for the N9 again. If they're not too high (600 Euros for a smartphone - honestly, I could get two Android phones for this price), I will either buy a N9 or wait for Tizen to see what it can do.

So my advice for you: Currently, we have a bad time for switching smartphones - you should wait some months before making a decision.