There are several earlier threads on this subject if you search for them. I bought mine at 109,000 miles and 4 years old. It has required a new N75 valve, an exchange MAF, CV joints to both front wheels and a bearing, and a new wiper motor. Brake pads replaced once so far. I get the 4 wheel alignment done regularly, some people don't realise the rear wheels can be aligned on a quattro, so check. The cam belt has been changed with all the associated pulleys and ancillary belts at the specified 80000 mile interval. All the electrics still function ok, except problem in last few weeks with air blower. Leather interior is in very good condition, and all the lights cupholders ashtrays ciggie lighters seat adjusters seat belts load covers dog guards you name it all work fine. You should not expect less unless it hasn't been cared for, in which case walk away and find another one.
I have chipped it with noticeable benefits, especially to the low revs response. As i was doing a high mileage i was using the long life services but have now reverted to the 10000 mile interval as i am below 30k a year now. Tyres last 15 to 22000 miles depending on opoen road or motorway use, Goodyears are grippy but wear out, Continentals are longer lasting but not quite as good in the wet. Have averaged 33mpg to date. Engine failed at 174k due to oil pump failure but this does not appear to be a common problem. Rebuilt back on the road and up to 184k at nearly 7 years old. This is a long distance mile muncher, not especially nippy around town. If you have small kids or if you do a lot of suburban driving consider a 1.9tdi A4 Avant that has been chipped . If you have big kids and or long journeys you will struggle to match the A6 Avant. If you go for the 2WD the economy will be much better but once you've gone quattro its difficult to go back
