Quick answer to that is lease :)
If you have a good dealer, it's not difficult to swap out for a newer car when it becomes available. Often time with Audi cars, especially newer generation ones, the pay off price to outright purchase the car is less than what the car is actually worth on the market. My dealer even showed me some examples when we were trying to locate a car for me. I was really surprised at the gap. You could even turn around and sell the car and make a profit if you really wanted to.

Also, it may depend on whether you're going to get another A4 or an S4. It will probably be a while longer before a B9 S4 hits the street. Just food for thought. I actually had the same dilemma when considering what car to buy and I just pulled the trigger on the B8 S4 because I loved the looks and how it drove. Not going to worry about the next generation B9 platform.

i dont like owning these cars out of warranty or out of date. (i usually want or like the newest version). so i dont keep them past 3 years these days.

+1 :)

I finally pulled the trigger and ordered a 2014 S4 a few weeks ago. I've been on the fence since 2012 on whether I should let go of my B7 S4 for a B8 S4, but the fact that the Rear Power Sunshade is not available in the 2015s was what pushed me over the edge. Plus, I would have to wait 3 years (assuming the B9 A4 actually gets released next year, and the B9 S4 follows a year later, and allow for 1 year to get first year gremlins out) to get a B9 S4, and I couldn't wait that long.

I plan to keep the S4 at least until the warranty runs out...unless I have alot of trips to the dealer for service. I will get rid of it sooner if I do.

whether I keep the car longer depends on whether you can still get a manual transmission in a new replacement...or how good is the DCT at the time. Don't even know if my and wife's health will be good enough to drive a manual in 4 years.
so far, my wife will not drive anything but a manual.

An S5 convertible could be tempting if it's a hard top conv.

Best

I keep a car at least 10 years or 100K miles. That's why i got a Sirius lifetime subscription on it (the wife wanted that!). Only reason I wouldn't keep it at least 10 years or 100K miles would be if it was in a bad accident/wrecked (unless I win the lottery that is - then it's a new P car!).

im thinking forever ;-), or till I have to put more money in repairs than I should

This is true. I lease my cars and I had a 2011 Q5 that I was leasing and I ended up getting $6500 back in equity when the lease was up. The residual was a lot lower than what it was worth so I made out and was able to put some of that towards my S4. If you tire of cars quickly leasing (at least Audis) is not a bad idea.

Agreed except that anyone who leases is paying for the lower residual with higher monthly payments than competing brands due to the lower residual. Audi effectively transfers the risk of residual value to the lessee by collecting more than enough "rent" during the lease term and providing opportunity for equity at the end of the lease.

I'm not being critical as I also lease (tax reasons / self employed), but generally speaking the lower residual is not attractive to most who lease to minimize monthly payments. We may have equity in the lease at end of term or be able to trade in early but we are paying for it monthly.

Not sure I'm understanding your comment on residuals on Audis. As far as I understand, the residual on the S4 is pretty high, not low. In other words, the car is worth a fairly large amount of money after say 36 months, especially when comparing to BMW or MB. I may just not be thinking clearly and missing the point, lol.

The actual residual value may be high but the residual value baked into the Audi monthly lease payment is low. That's how you end up with such a high lease payment (and equity at the end of the lease). Residuals as a % of MSRP (as used in the lease payment) are higher for BMW's, Lexus, Infiniti, etc. which helps lower their lease prices. However, there is no equity in them at lease end and it is harder to trade them in early because they aren't worth more than the payoff.