I too liked the 06 STi that I drove before, but also had the chance with a 11 STi as well, quite nice for daily driving. Regardless of your choice, you can't go wrong. With that kind of budget though, your fairly close getting a newer one. Newest WRX is pretty practical, gas mileage is somewhat decent so daily driving will be good. The tune on it though was greatly fixed with Cobbs Stage 1 map though, which makes it pretty darn quick for the money difference between the WRX and STi.
I wish the STi got that twin scroll turbo
But I'm aiming for the 15 STi here in about 2 weeks for the pre order.
If you can somehow squeeze out for a newer one, at least you'll have the peace of mind knowing it wasn't abused or modded prior to the sale.