I'd be interested to hear about standard 2.5 engines going wrong if looked after, as other than the bad map issue on the early hatch, it seems to be those played with. They don't appear as strong when pushed.
The poor rep of the 2.5 goes way beyond the reality in my opinion.
That said, I agree with Steve about which Impreza I'd want, although I'd add the R205 to the list!
The 2.0 in my wife's WRX PPP blob Wagon seems a bit more eager low down than my FSTi (with a 2.5), but then the map, turbo and different gearing has a say in that too!