Good questions........
when I bought the Turbo S in October I wasn't looking to change!! I went up to my local OPC to collect some parts for a 994 S2 I was selling and noticed it on the stock list. My C4S was a regional concourse winner and even if I say myself was absolutely mint and low mileage so it was a bit of a wrench to part with it. That said the Turbo was a one owner car supplied and serviced by the OPC and was low mileage too, a test drive soon had me hooked and the deal was done quite quickly.
The performance from the C4S is obviously up a few notches especially with the X50 pack, plus the combination of the PCCB and hollow spoke wheels conspires to make the steering lighter whilst no less planted. My intention is to keep the car for some time as its not my daily drive, that task is undertaken by the A5 diesel I got when I went back into the company car scheme on acccount of the increasing business mileage I'm doing right now. After 2500 miles in 6 weeks in that I can't wait to get the cover off the turbo and drive her again I can tell you.
I'm firmly in the, 'you only live once camp' don't drink don't smoke and work hard so justify it to myself and probably more importantly SWMBO on that basis. All told I would do it again but I don't spend hours thinking about the depreciation, the original owner took the biggest hit in my opinion . The other thing I've come to realise is that there's always a new model just around the corner and keeping up with the latest technology and performance will always be expensive. When I was growing up I always wanted a Porsche 911, never thought I'd be able to afford one, and since since getting my first a new Boxster S in 2003 I'm now on my my 4th, (5th if you include the 944 S2 I had as an itch that had to be scratched) Whilst all have been superb cars the Turbo S in performance terms is on another level whilst still very useable. On that basis I intend to keep her for the foreseeable future.
hope this helps