The problem isn't mechanical longevity; T-series cars are outliving their owners, a situation which will only get worse. An enthusiast today who is 25 or 35 years old might find a TC or TD cute or quaint, but they probably won't find them desirable once they discover their lackluster acceleration and limited top speed. A TC is beautiful to look at, but it isn't much fun to drive in modern traffic. It's at its best following a meandering country lane at 45 mph. The people who grew up with these cars accept such limitations. Without this perspective, an anemic 50-year-old-car is an anachronism.
Almost every organization specializing in old cars faces the same problem: how to attract younger members. Prices have risen so that a basket case TD costs over $10,000, thereby preventing young enthusiasts from indulging.
MGAs are following closely and it won't be long before MGBs are out of reach. We can only hope that the charisma of MGs and the friendly nature of their owners will alter what seems inevitable: in another 20 years there may not be many of the MG faithful left to gather.