And an extrovert trying to become an introvert would probably find himself incredibly bored and lonely. They're just two different orientations, we don't need to be constantly asserting superiority over one or the other.
I'd say that "it's probably best to be somewhere in the middle, so that you're neither worn out by social situations or bored by spending time alone" but there's probably enough self-aggrandisement in this thread already.
As for not being able to change however, I don't believe that's set in stone. I took the test about 7 years ago and since then I feel like I'm more like 65%i/35%e. The whole idea of charging however is strange. Though I felt back before the test that i could only recharge at home, alone. At one point while i was the most social I felt as if I had to charge at home, then go out to recharge to balance it out. The brain is a very strange thing.