I think most of the difficulties are attributed to the type of running the car has had, as opposed to the previous owner's driving style (after all, most brand-new cars are sold to fleets as either company cars or hire hire/lease cars, therefore this trickles down throughout the second-hand market).
When I was with Ford, I noticed a trend, it was the low annual-mileage cars (used primarily for short, stop-start journeys) that gave rise to the most problems. Things like clutch/brake and exhaust replacement at some pretty low mileages. I think that motability cars tend to fall into this category (much like ex-channel island cars), and are mistakenly interpreted in the following way; lower mileage = less wear & tear = less problems = more valuable car.
I wouldn't like to say that all the expense (of the unforeseen variety) is behind you - you may keep the car, and something else fails, or you may sell your car (probably taking a financial hit), only for someone else to reap the benefit of your expenditure to date.
Its a situation we all face - every mile we travel in our cars brings each component closer to failure.
Whatever you decide, try to ensure that you don't make your decision in the heat of the moment.