I'm really feeling what Penfold is saying here. My 5 is similar to your's; mine has recently pipped the 20,000 mile mark and it really is like a brand new car.... but........... is it practical? Is it fook!! I have contemplated getting rid off mine a couple of times for the exact reasons Penfold has mentioned and in turn buying something I can use care-free.
Finding OE parts at the moment is still achievable but its going to get harder. I disagree that 5's are only going to be on the road for the next 5-10 years max. Enthusiasts keep other classics on the road [Ford, Merc, Jag] so I don't see why R5 owners' would be any different, I mean that's what RTOC is all about.
But I know if it came to the crunch I couldn't let it go. For me personally I have a long history with these little hot-hatches and my tungy is part of the family. Last year I sold my OE white 5 [pics on my profile page] because I needed the cash... do I regret it.. damn right I do. However the guy I sold it to was real stand-up and a real 5 enthusiast (he's a club member) which makes the fact that its gone a little easier to deal with
From one minty owner to another... my advice is to keep, keep, keep. If you really do want to sell make sure it goes to someone that's going to treat it with total respect and preferably, keep it in the club.