mike
i've done similar thing as you're looking to - i handed back the company car (golf gti - comfortable, all mod cons, free tyres & servicing & insurance [

]) and bought a 968 as my everyday car - the only difference being i only drive 10 miles a day
Like you i wanted the clubsport - and it had to have the proper bucket seats as opposed to the comfort spec ones - I appear to suffer from some sort of lightweight porsche fetish [8D]. This is (warts 'n all) what its like to make the change:
Its been 6 months now since i swapped. i bought a 1 owner since new car with 70k miles on it and full history (including bills for work done, not just the oil changes). i also budgeted to change ALL belts & fluids immediately for peace of mind - and also had to spend a bit on a tiny oil leak a the same time. Makes sense to put by another £1-2000 to 'fettle' the car you buy - especially if you are a bit anal about having the car sorted completely.
Day to day its uncomfortable, and i look like a drunk driving around as i'm continuously swerving around potholes - suddenly you realise how bad our roads are. having no air con was a bitch in the summer for about a week. no central locking is a pain when its raining. opening the boot from the passenger side only is a double pain when allied to no central locking - especially when its raining again! the seats require an advanced level of gymnastics daily, but are comfortable as long as you don't have anything in your trouser pockets for the majority of the time. when you're stuck in traffic and its hot however you end up with your trousers tightening around your nethers and you can't move around as the seat is holding you in so tightly...then it can get painful [

]. i'm also paranoid about parking it anywhere, a bit self concious of having a bright red phallus replacement - especially sat in traffic on the way home as i'm doing some sort of disco shuffle trying the re-arrange myself with transit drivers looking down at you, i get annoyed about parking dents in the doors, it uses more fuel than the golf, and i'm constantly paranoid about every noise the car makes expecting the worst and a massive bill. Having no rear wiper and no heated rear view mirrors means that backing out of my driveway every morning can be haphazard. being unable to adjust the wing mirrors from inside the car is a pain when you've washed it and go for a drive forgetting to reset them. winding down the window manually is fine, but not being able to wind down the passenger one electrically can be a pain in the ar5e. only having two seats means its totally impractical when you have visitors - especially if the wife has a two seater as well.
Where the company golf was indestructable - it never needed oil or tyres checking, could be left in any side street in london, could be driven at ten tenths everywhere in front wheel drive understeer mode, fitted through every gap, was happy bouncing over kerbs and never needed a cover in the boot before going to the tip, the 968 needs 100% concentration - especially in the wet on the motorway. it needs all oil and tyres checked every week and is probably driven slower everywhere. it really needs a total shift of mindset.
would i swap back therefore? NO. i love my 968. all of the stuff above is the character missing in modern euroboxes. having to think about driving i reckon makes me a safer driver as i'm alert all the time. theres pleasure in how well the car is engineered vs a modern car - just look at the quality of a new ford's interior. the sensation of flooring it past traffic on an A road and having more than enough power to do it safely. its practical enought to fit a christmas tree in the back. i take stuff to the tip in it (with a heavyweight tarpaulin covering the carpet!). i'm still learning the limits of the car 6 months into ownership (as opposed to 6 days in the golf). its rare - you hardly ever see any on the road. people who know their cars respect your choice. hopefully its not depreciating too much.
overall therefore - go for it. i don't reckon you'd lose too much having 100k on the clock vs 70k as long as the car had been maintained. alternatively go for a high miler now as there will be less price differential between a 100k and a 120k car. be prepared to spend money on it - however my calculations reckoned it would still be cheaper than the depreciation on a second hand car (example: the wifes Boxster has lost approx £10k over 3 years and we bought it second hand [

]...)
the final way i justified it to myself was that if it did'nt work out i could sell the car, take a £2-4k hit and return to the company car scheme having learnt an expensive lesson...but its always better to regret what you have done than what you haven't.
best of luck
Matt