Here's something else to consider:
A high resistance intercooler will make the turbocharger "feel" like it's at higher boost than it actually is. A restrictive intake does the same thing. On a performance car this is bad, but on a stock car that's not necessarily the case.
I have a 2002 Saab Viggen which at peak hp runs roughly 13 psi of boost pressure. However the stock compressor for the car is most efficient on the high flow side of the map at a pressure ratio of 2.5:1. If I had no intercooler backpressure, no intake restriction, and no other flow restrictions my car stock would only cause a pressure ratio of about 1.9. This means that Saab engineered the parts to create some resistance so that on the stock vehicle it should always been at a "good place" on the pressure map.
Of course someone will always tell me to put a big intercooler on my car, and I won't argue! The moment I crank the boost up even a little I would be well advised to have one. But keeping everything else stock, the benefit from an $800 intercooler would be very little. Nowhere near that of say an $800 turbo back exhaust.
As Brad said, there are a lot of things to consider. I would actually reccomend a larger intercooler! But I just wanted to post that stuff so that anyone with a stock car doesn't go out and waste $800, unless they've considered all of the variables. 90% of the time it's probably not necessary.
Adrian~
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