I have been giving this some thought lately.....I have had my 2000 facelift coming up for 2 years.....I bought it with 40k miles and it is now just north of 50k miles...recent mot and Goodyear F1's......it is spot on!
I have considered a B5 Rs4, but for similar mileage I will need to spend another £15k and then I will buy a car which may have problems to sort, plus I have known my S4 known since new, other factors such as the anonymous stealth aspect of the S4 all weigh in it's favour.
Thankfully the cost to change isn't so much a problem rather than hard to justify,,,,,,I could buy a caterham or elise with the difference,,,but then i already have a perfect trackday porker and classic drophead for sunny sunday pub lunch runs...
I have considered an MRC remap for the S4, but then again it is currently £280 a year comp insurance and I do 5k miles a year..
Having gone through all of the above, I will probably just keep the car, it is becoming like an old pair of favourite shoes
I figure the depreciation over the next 3 years is minimal by which point a B7 RS4 will be available at sensible money.