It was a really good car, as long as you don't need anything too practical. The back seats aren't great, nor is the boot, but its a fun car to drive, and its quick, it only weighs about 1300kg so it feels nimble and "chuckable".
We drove down to the South of France in it for our holidays last year, and it coped really well, although i don't think the seats are as comfortable as those in the TT.
We had ours for 10 months from new, and we averaged about 40 mpg, we had the TLC servicing pack for 5 years too, and i think road tax was £135 per year, so it really is an affordable quick car, just the initial purchase price which seems steep compared to many other cars.
We didn't have a single thing go wrong with it while we owned it. The only thing which lets it down is the run flat tyres, they crash and bounce all over the place. I think they come as standard only on the Cooper S, so if you get a Cooper rather than an S, you'd be okay. If we'd have kept the car longer, i'd have put normal tyres on when they needed changing.
All i'll say is go out and get a test drive, and see what you think. Our car was a Cooper S with Chilli pack, chilli red paint, 17" alloys, half leather/cloth, heated seats, and that was pretty much it, and that cost about £18.5k, but had everything we needed. You'll find many 2nd hand cars that have been specced up with £6k of extras, we just didn't see the point!!!
I have to say, if we were looking now, and spending £18.5k, i'd be sseriously looking at a used Mk5 Golf Gti for the practicality, or even waiting for the new VW Scirocco, which i think is starting at that price.
To sum up, i'd happily have another one, i just don't think they're a practical prospect if you have kids, certainly no more practical than a TT coupe
