CappAttack, hope you're having fun fixing and repairing the car back up to snuff.
1) Intercooler mod - add a drain.
Some of the mention of the intercooler made me think of something I saw some time ago, that I did do to my second TDI to avoid oil buildup.
ThomasEXOVCDS Pointed this out in his wealth of VW repair videos, that just drilling a small hole into the bottom of the intercooler and using a screw to seal it.
In my case, I used one of the many many T20 exterior screws I've acquired while on runs to the wrecking yards to replace parts on my car. As in, the T20 screws that are used to hold in the inner fender liners on the car.
I can't say I've had hordes of oil drain from the intercooler in this car, I did it more for peace of mind -- something I can check and drain, when doing a major maintenance, like an oil change, tire rotation, or timing belt change.
2) Skidplate
DO-EET! I lost three (3) oilpans on my first TDI; one to a slow leak scraping, two to catasphrophic impacts. The oilpans are fragile, and since yours is a bit higher mileage, the suspension might not be at full height, which leaves your oilpan hanging lower than stock.
If you're intent on getting another 200k miles out of the car, the skidplate will cost you as much as two oilpans and oil changes, and might save you an engine.
And not a mod, but another suggestion - in addition to TDIclub,
www.myturbodiesel.com is worth signing up for a forum account there, if only for their timing belt change writeup. They also have a decent buyer's guide for the A4 platform (Golf/Jetta/Beetle) that might give you more ideas for things to check for maintenance wise.