I was asked last night this question, now normally I wouldn't take much into this question but they were actually interested in the answer. So here is the question and my answer:
If Transylvania wasn't ever really a "country" of its own and over the course of hundreds of years was a part of Romania or Hungary or some other country, why is it important.
It's important since it never became a hotbed for violence, there were many great people who came out of that area, changing the course of history. It is a legendary place, both in history and in fiction. The center of the land was fertile and was a pathway to Europe. Everyone-- the Romans onwards wanted this land.
That's why it's important.