The thing that MGs (and presumably a lot of other old cars) can offer that a Miata can't is the thrill of driving away from a breakdown. Nothing gives me greater pleasure than having my old B break down somewhere, and getting out of the car, figuring out what the problem is, fixing or temporarily jury rigging it, and driving on... Good times. I don't care that it often takes me six hours to get from Portland to Seattle. None of my friends understand.
(Of course, there are also the heartbreaking tow-truck-required breakdowns, but I try to put those out of my mind. )