i bougt my wrx with full history but when looked on stamps main at 50k miles was other- from some garage which i checked but was not exist, they can give You book with stamps but they should have recipe what was done to.
really main thing you can check is suspension,gearbox,clutch, rust ,engine bay/leak, tyres, brakes but still you miss something.
new alternator could cost you 300 out of pocket in seconds, not many check it
even if you buy it without history then price is lower and you easilly can do it yourself
i mean cambelt,fluids and filters, brakes, tyres,sparks.
no matter what kind of history it has lf owner dont top up oil on time - thats main thing with UK owners.

 

Go test drive some, I originally had a my03 blob wrx and spent a bit of money on it getting it to sti spec, then after that bought a my05 jdm sti, other than an exhaust change to my liking and a map check over I haven't had the inclination to do anything else and now realise I should have stumped up the extra in the first place. But the sti is more hardcore, better brakes and much firmer ride so it depends what you want, my old wrx with exhaust and remap on td04 was no slouch and I have no regrets owning it, just I wanted a more hardcore car so changed it. The wrx is a better daily driver though especially for passengers as mine complain about the ride in the sti whereas in the wrx I had no complaints.