Hi V28 - As a recent purchaser - I would give you my 2p!
Of course you should buy on condition and maintenance history rather than spec, miles or age, but I have just bought a 2015, ultra low mileage (21k), well maintained car with a few condition blemishes, in a mid range spec, but with full Audi history.
Budget went from £25k to £30k+ in a matter of months as I realised what I got for my money. However, even paying an upper end price, I've still had to spend quite a bit of money at the 6 year anniversary service when coolant, spark plugs, air filters and all 4 of the transmission oils need to be changed on top of the inspection service (with engine oil, brake fluid, aircon etc). I am also going to get a specialist look at the DRC system (although mine does feel particularly "tight" on the suspension front).
Tips are buy a car that either doesn't need (or has recently had), all of it's tyres, brake discs and pads changed. That's a huge bill otherwise. Same applies with the DRC system where if it's had shocks and pipes changed, you are probably safe for a while. I can't advise on a car that's had coilovers fitted, but others on here will be able to.
The spec is pretty good as standard, but everyone has their likes. Essential for purchase / resale seems to be: Sports exhaust, 20" wheels, heated seats and the B&O sound system. Nice to haves are the reversing camera, the seat & mirror memory, radar cruise, keyless entry, high beam assist, the styling packs and the pan roof.
The cars are also colour sensitive, with white and red being worth less than black, blue, grey and silver. The Nogaro Blue Edition cars command more money, but the spec is very basic and although I love the interior, I'm not sure they're worth the premium they once enjoyed.
The dealers (independent or manufacturer) add a lot of money to the price for very little (typically 15-25%), although Audi will throw in a good 12 month warranty and can be haggled into providing 24 months (rather than discounting the car).
Personally I think the best prices and most choice lies in the Private sale market and I bought my car off a forum member who had a lovely car and was a super honest and genuine guy. Although recently damaged in an incident with a twonk in a van - I can't wait to get her back.
RS4 B8 - Sepang Blue, Black Leather, Aluminium Pack, 20" V-Spokes.