Lots to consider, especially in the UK with Road Tax likely to keep on rising.
Insurance doesn't seem to vary much between models.
Depreciation is nil if you keep away from new.
So in no particular order............

Cost of Road Tax
Complexity of electronics
Long door or short door
Stainless bulkhead or steel bulkhead
Traditional hood or easy up hood
Exhaust noise
Spare wheel or no spare wheel

My recent experience of Roadster vs Plus 4 - on the motorway no difference. Plus 4 is sharper off the line - lower geared.
Plus 4 sips fuel in comparison to Roadster (which does 30).
Roadster has better exhaust note above 4k revs and flies above 4k revs, but in most situations there really is very little difference.
I've toyed with a Plus 8 for a long time, and miss the exhaust note of the Rover V8, but for now I'm happy as I am.



DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4