mmm, leave them but sell the other bits that you didn't have to drill/hack the car to fit (hard top / windstop). I'd stick it on autotrader for £15, prob a good time of year to sell (once we get some sun!).
I've just bought my TF for not much more than they've offered you there, with 22,000 miles on it. I wouldn't be surprised to find that some, possibly less knowledgable, garages see them as a liability thanks to the collapse of MGR. Personally I think that's daft, but it might be worth shopping around if you'd prefer a trade in, if you can?