I am with you on the mileage issue, indeed I would see such low mileage as a potential issue, at 3k miles it is possible that the S4 has not yet been fully debugged and of course is now well out of warranty.
Out of curiosity what are the multiple updates on the S4 over the S3 apart from an extra 400cc of course. I recall that the rear tank was re-positioned reducing interior space but increasing boot size, different colour instruments? a conventional hand brake (for me these are change rather than updates). The S4 is very well specced but I have always understood that for high end cars, having all the toys makes them easier to sell rather than increases the price. The colour is also a little challenging.

The big advantage that the S4 has for me is that it an Auto, making it the only Aero I could personally consider now and of course the other argument for the price is "try and find another one"

Brian