While most enthusiasts would swear by the RS4 as the best quasi-affordable car in the Audi stable, I would suggest that the S8 is the best blend of performance and luxury.
Take the SWB version of the A8, add a 450hp V10, dress it in carbon and tighten the suspension up significantly and you've got the S8. Perfect for the enthusiast that wants to carry passengers and still open it up a bit.
The W12 and V8 Phaetons are hidden gems in the luxury car world, vastly undervalued but more option packed than even the best S-Class or 7'er of the day. Available for under $35k, these are hard to pass up for a want the best in understated luxury cruising. Brand-snobs need not apply.
The rear spoiler can be tricky. It will normally drop while you hold the switch after starting the vehicle. We have a few customs that had the same problem and I believe there is a software update that might help.