There are a number of things you get on an STi which are worth the price over a WRX - 6-speed, DCCD, Brembos, stronger engine internals and a bigger turbo.
It all depends on budget and what you're after, I've just bought a new turbo for my WRX since the standard TD04 was reaching its limit.....if I had an STi I could probably keep going with the stock turbo.
I think I said it in the thread about my car, but I'm happy I bought a WRX and can now make it individual with the money I saved rather than getting an STi and keeping it stock as I spent too much on the base car. For what I use my car for its more than capable, an absolute blast to drive and will stay with a stock STi as it is at the moment.....give me 3 weeks and it won't see which way I went.