TBH it looks lovely and in good condition for the miles.
But with the price of roadsters £11k will get you a 85k or less car, market seems slow probably more room to move at that price too. Depends how you look at it, looks good money if you decide to keep it as is and just run it, not worry enjoy it as intended.
Inevitably it needs some work due to miles and age and with the other issues like the roof motor and maybe some body work, refurb 224s and some new tyres (but sell the other wheels to pay for that), you could easily spend £2k.
85k vs 140k its 40% less mileage for 18% more money and you get to do that 55k whereas that car would be knocking on the door of 200k.
If you have a look at threads like this:
http://www.m3forum.net/m3forum/showthre ... 14&page=34
It does fill you with confidence that with normal maintenance the S54 will easily hit 150 if not more. Whether the little whisper in your ear about the possible failure is worth the risk. 9k is still 9k for that money a well fettled 3.0SI may be a better choice.