The RS4 looks cool stood still, but is still a quite a heavy estate car, and when not in the turbo, is quite tame, they are quiet too in standard trim, so you don't get the same blast experience you do with say, a CSL.
After buying the Porsche and driving it 2000 miles, I decided that it would be better to run it at the weekends and special days, 1. to keep the miles off, and hopefully help it hold its price, and 2. they are quite stiff on the bumpy lanes, so a bit of comfort is needed as one gets older.
The RS4 is very good car, but I found that it as it was a comfy estate, it felt more like the practical daily than the C4S, though the manual gearbox, and 21 MPG meant that for me that wasn't possible. Plus the mileage really affects the price.
As for the next car, sadly as I have now bought my Mrs a small DS3, I have settled for a E92 325D M Sport Tourer for my daily and dog vehicle (in essence replacing the RS4), and the C4S will be the special one, shame its not a Turbo, but I think I'd kill myself, as the C4S is quick enough when you hit the loud peddle.
Shame the CSL's have gone up gain, as that would be the C4S's natural replacement now that my 911 itch has been truly scratched.
RS4 - Sensible replacement. Low power 3.0 Diesel M Sport. For work, dogs and wallet.