I just purchased a '91 Audi 80 with 178k miles. Runs very well, and is still in quite good shape. I paid $325, so I'm willing to put a little cash into it for improvements. I will be installing a new starter this weekend, as well as the below items:

air filter
oil filter (and corresponding oil change)
spark plugs
distributor cap/rotor
wire harness

Just wondering what else you think I should do. Do Audis have a propensity to have anything in particular go wrong that I should be watching out for? In other words, Saabs often have problems with the idler pulley and the direct ignition cassette--does Audi have any similar I should look out for?

Don't forget all your belts especially timing. Water pump and belt idler/tensioner is one more area to check. Also check for leaks, older Audi's are notorious leakers. If it's liquid it will probably leak. Radiators and heater cores have plastic sides and are prone to cracking. Expansion tank is another, like I said check for leaks.