A lack of VW trim pieces would be nice! [:-]
As for the rest:
Half a cayenne V8 on the front, belt driven of course. 3(ish) litre 16v, maybe with twin sequential turbo's. And spend some money on the damned wastegate this time! A bit better organisation in the engine bay wouldn't go amiss, but no tacky plastic covers to prevent anything but adding washer fluid please. Obviously updated management too, which may or may not include MAP. Should be easy to chip too!
Update the interior. Definately some more modern switchgear and lighting, and a much more modern gauge set, but none of this 911 look please. I can't stand that "stacked" look. It dates so quickly. Add in some decent driver info in the cluster too (or at least a clock!) It would be nice to think they could get the dash so compact as it is now, but I guess with all the current regs (for saving dumb-a$$ drivers from themselves), it won't be easy. Some more sporty seats would be cool, basically padded, reclining/tilting shells would be good, and thin down the rears. They're not a lot of use as it is, so have them there for sure, but not so that people would actually pretend they can go further than round the shops 4-up! Lot's of leather though of course!
Keep the sunroof as it is, but maybe add a slid feature in a-la Calibra where it tilts up a tiny bit, and slides over what's left of the roof. It still needs to be removeable though. Oh, and SORT OUT THE GEARS!!
Update the suspension to Double-wishbone all-round, which at least dumps the torsion bars, and adds some coil-overs on the rear.
Definately add another gear to the 'box, keep the LSD though.
Add run flats so you can dump the spare too. Don't like that weight!
Rig up the rear spolier so that it rises or tilts with a speed incease too. I liked that riceness(!) on my old Corrado.
Then all it needs is a general update on the styling. Not too much as the general look of the car (I think) has aged very well, but a few more modern touches like better mirrors/handles, and a general De-locking of everything tidies it up nicely. A bit more aggression to the front and rear lower ends wouldn't go amiss either. And bigger wheels of course. 19's seem par for the course at the moment (ducks!)
Oh yeah, and definately add better headlights. Keep the flip-up's, but maybe go twin-pods, and sick in some HID's (none of this self-levelling rubbish though! The jumping annoys the hell out of me on my Dad's Renault!
Last but not least, DON'T offer it in America. I know our firend's over there would be disappointed, but with all the stupid regs over there right now, it would compromise things too much. Sorry guys!