nice car, the looks are far better than the mk4 but performance wise the mk4 is in another league. and I'm talking both chassis and engine.
Only thing better is that the mk3 is lighter. altho I've talked to more than one person in here that preferred his old mk3 to his new mk4 so who knows?
there are about a thousand lil things that can go wrong on these cars but it's about the same on the mk4 and they can surely do better than most other brands [bar the japs].
things I'd check on a 55k miles car would be:
-turbo [it doesn't have to whistle too much,,, if the car isn't mapped you almost shouldn't be able to hear it]
-clutch [it doesn't have to slip and you shouldn't be able to hear the release bearing when you press the pedal while changing gear]
-gearbox [check how the synchros work, that all gear engagements are ok and that there's no odd noise]
-general overall interior condition [the plastics on these cars are utter crap and they cost quite a bit to buy new, the steering wheel will almost for sure be badly worn, check the seats and the gearknob]
-steering and suspensions condition
that would be amost all,,, plus what stew said. check also here:
http://www.samarins.com/ for good guides,,,
now I don't want you to get paranoid about it. I got the car since 2002 and I'm quite happy with it. remap it and the performance is decent, if you want something more then it's ££. fuel economy is very good in non-city driving, decent in the city,,, surely much much better than an equally powered petrol.
Feel free to ask questions.