Who knows what's next... If you're lucky enough and of course keep on top of maintenance, perhaps nothing?
Obviously cambelts, water pumps and things like that will need to be replaced again at some stage; but as that's all been done recently you should be able to forget those for a good while. In terms of other wear and tear items I'd say you might need to be looking at suspension next time, as sooner or later it's going to get tired; but other than that I guess it's just service parts unless you're unlucky.
On the issue of keep it or sell it I think you've already answered that one yourself... "I love it to bits." If you can confidently make a statement like that; I'd say hang on to it until either a) it no longer meets your needs, b) it's not financially viable to keep it going, or c) you just don't find yourself 'loving it to bits' anymore. Plus I guess that if you've owned it since new the best way you can maximise the value of your purchase now is to carry on driving it until either 'a' or 'b' (and to a lesser extent 'c') above...
Anyway, roll on '98 A3s! Mine's a '98 too, 52,500 miles young, and still going strong; and OK, given what's under the hood it might not be the most white-knuckle style exciting car in the world (or even posted-about on this forum within the last 2 minutes) I enjoy driving it - and when my front bumper's resprayed I'm sure I'll enjoy looking at it again too...
I say the best of luck to you for trouble free motoring, and may you and your '98 A3 live happily ever after!
Regards,
Rob.
