Just bought a 55 S convertible auto, very well spec'd, from a main dealer in Surrey (I'm near manchester!). Drove it back today.
I only managed to negotiate a (full!) tank of petrol and 6 months tax over the phone - nothing else - but the spec is what we've been waiting for. Appeared on the mini used website this week, less than 48 hours later the deal was done (without even seeing pics of the car) subject to actually viewing and driving it. It's taken maybe three months of looking to find the spec, colour etc we want - if the cars you're looking at aren't 110% what you want, wait, one will turn up.
The main dealer thing is worth it, from the cars I've seen outside of the dealer network, it's safer (and in our case a good £1,000 cheaper!!!) to buy mini cherished. Warranty, breakdown cover, all adds up, but they pitch them fairly low to sell convertibles at this time of year.
Of the cars you describe, I'm with the hyper blue one - the genuine
JCW bits will help keep the cars value up, and it's possibly a more desirable colour than the purple - personally I think the hyper blue is the best colour they've done, why they discontinued it I don't know.
Best of luck!