So I figured I'd update people on my experiences with trading in my car and choosing an STI.
Basically I shopped around a bunch, I even was about to buy an Evo X 2008. What I found though is that my issue wasn't so much getting a fair price on my WRX, most people didn't even know how to price it because there isn't a market for used 2010 wrx's yet. No one is selling them used haha. But most feel like since the news of the new wide body wrx's and such that any of the older ones, wagon or not, will severely drop in price.
I think what I am going to end up doing is private party sell my wrx now. And just save up my money for a 2011 STI, or buy any of the 2008+ STI wagons since they will also drop in price due to the sedan.