Cooper S or JCW?

Now I have sold my 130i and have the new to me '54 X3 3.0i as my 'only' car (which is surprisingly nippy), I am thinking about a fun 'runaround'.

My wife has her beloved Cooper (30k miles since she bought it new in '03) and I do enjoy driving it but would prefer a bit more oomph.

So the consideration is to an S or maybe a JCW - up to £7k.
It would be used for local journeys and work stuff in the south east but the longer journeys and load lugging left to the X3 (which also tows my bike trailer).

I dumped the RFT's on the 130 as the ride was appalling so what should I look for in the ride and servicing departments for either car?
I have no experience of the supercharger, either from a driving point of view or from a servicing/reliability stance. I was a bit disappointed with my year in my supercharged Corrado way back and changed to a VR6 but that's no real comparison - I am not a fan of turbo's though.

Will either of them feel like riding a rigid chassis on our grotty south east roads - very little motorway driving envisaged.

Is there a mileage where things start to become risky?

Any useful thoughts gratefully received.

Cheers
David