While I have never seen or heard a TLM, I would welcome a wider availability, even if I never do go to one. Likely not every parish needs it, but I would think at least every major city should have it available on all Sundays and Holy Days of Obligation. That is just an opinion.
As to those that blame the down-spiral in so much of the Church on the change from the TLM to the NO, I don’t think that is at all correct. While the timing is very similar, I don’t think you have the correct cause identified. After all, you can’t blame the change in the mass for the giant changes in culture, government, family, education, etc that happened at that time period. Ultimately there had to have been a serious break down in the way the faith was handed down, prior to the change in the mass. If everyone had been properly instructed regarding the faith and the mass, I doubt it would have been accepted.
My personal theory is that it was probably a back to back global depression and a world war that simply applied too much strain, for too long, on families and all the institutions that make society function. I think the change that became visible in the 60s and 70s had its hidden roots going to those earlier times. This isn’t to say recovery wasn’t possible, after all societies have come back from worse. Yet, there was also an influence from many misleading ideologies, and so radical change became the norm across all parts of society. Of those things that did not change, some were destroyed, others remain still as hollow shells of a once grand past.
As to the Latin itself, I doubt most understood it. Many likely new the responses, in the form of memorization. Even the vernacular translations would be easy to memorize. However, the number that actually new Latin well enough to really understand the complexity and nuance in the liturgy was probably quite small. I took Latin in high school, and I am currently taking it in college. I can attest that Latin is by no means a simple or easy language. I suspect if I went to a Latin mass I would understand at best one word in four by hearing. As to being able to actually translate mentally, that is well beyond my ability. Simple greetings and such I can do. Study of Latin today is almost entirely of the written form. Only a small handful of places teach Latin like a living language and thus use its spoken form.
I can also tell you that Liturgical Latin is a late development, relatively. It was sort of a simplified, distilled form of Latin, then watered down some by introduction of local dialectic/vernacular variations. It is still an impressive language, but it is not quite the same as Latin of the classical authors (which was a somewhat artificial form for high literary purposes). The most readily observed change from classical Latin to liturgical Latin, is a shift toward Italian sounding pronunciation.
In classical Latin for example, the letter V would be pronounced more like the W in English (which is oddly the reverse of German, from what I understand).
