I also read about the chain stretch but it seems to be such a rare problem that you only hear about the 1 or 2 that do happen. As far as servicing is concerned if you have a decent independant mechanic you know then it is what they charge for the job.
For context I had a quote from Audi dealer Robinsons for the full works service, when I first got my 3.2, at around £540, my usual mechanic did it for £160 but that was mainly a standard service with no whistles and bells like Audi would probably throw in.
Mileage was 79k when i got mine, its at 84k now as I do so few miles in it second car and all that and I paid £5k for it with full service history and paperwork for all jobs done. As with most Audis its lasting well and I don't regret buying it as a stand in car.
In the end it depends what you want to do with it, it is not very modifiable if you want additional power. The stereo is pre smart phone and will probably cost to change from single din to double to get a lovely new stereo sat nav etc unit.
Small niggles however if you are not worried about power or you are not an audiophile. All in all it's a great cruiser and works well for me.