I can't see that in the UK, the Mini brand is one of the slowest depreciating cars in the UK (even less than a Boxster) Plus Glasses seem to love them (and the Clubman)
The big stickign point will come if Mini flood the market with them (no sign of that yet) and they only cars I'd mark down less are the launch cars, look on the Cherished website, there must be around 10-20 examples of the exact same car for sale at the moment.
I reckon the depreciation will be fine, on a par or better than the hatchback (around 70%), remember that all the extras apart from the Packs, Paint and TLC count for very little in trade terms. So a Chilli Clubman OTR circa £16k should be worth roughly £11-11.5k in 3 years time.
I still reckon the S will get hit the worst and the Diesels should excel, especially as Toll roads and Congestion Charges will be more commonplace in 3-5 years time.