Dragons vs. Balrogs?

[obloquy]

Hiya Kuruharan. =)

In fact, as I have pointed out (a few times) there are some good hints in the text that suggest that they did.

Tolkien was very clear about other incarnate Maiar. He didn't just hint at it. We know that Dragons didn't make their own hroar, which means that if their fear were Maiarin, their incarnation would've been a unique case: Morgoth was never spoken of as having created empty bodies to be possessed by corrupted Maiar spirits. Though this doesn't rule out the possibility, I think that if it had happened this way, it would be uncharacteristic of JRRT to leave it unexplained.

And there is no reason whatsoever to believe that they did not.

I don't agree with this line of reasoning. Unless there is some textual indication that they were Maiar there's simply no solid argument. You can make comparisons and draw parallels all you want, but in the end that's all you'll have. Granted, it's a very real possibility, but no more likely than Goldberry being Yavanna.