1st reference (1R):
"His enemy halted again, facing him, and the shadow about it reached out like two vast wings."

2nd reference (2R):
It stepped forward slowly on to the bridge, and suddenly it drew itself up to a great height, and its wings were spread from wall to wall..."

1R is clearly a simile, and has nothing to do with whether or not the balrog has wings. It is merely a descriptor of the terrible darkness associated with the fallen Maia.

2R is a statement that does deal with the presence of wings. It says they were there. If they weren't, they wouldn't be "spread from wall to wall."
There are also no indicators present in 2R to show it is an extension of the simile in 1R.

The way I see it, no other balrog passages can be used to support the debate with any respectable amount of certainty.

The fact that they arose and passed over Hithlum is ambiguous. Such an account could mean that they grouped together and footed it as easily as it could mean they leapt into the air and flew. Just because elves lived there at the time does not mean they had to witness the passing of the balrogs.

Gandalf's account of vanquishing the balrog is also of little use:

"I threw down my enemy, and he fell from his high place and broke the mountain-side where he smote it in his ruin."

There are too many variables left unwritten in this situation to make it's use in the debate as anything other than speculation. The non-wingers say if the balrog had wings, it would have flown to avoid crashing into the mountainside. The wingers say it was already defeated and thus unable to use its wings or any other ability it may have had to avoid impact. The words "smote it IN his ruin" do indicate that the balrog was already dead or dying as he fell. The passage does not say that the fall WAS his ruin. Regardless of the fact, the absence of any wing references has little meaning to the point of the debate.

The "tempest of fire" description of the balrogs' attack a little tricky. Let's look at two of the definitions for "tempest" as offered up in "The American Heritage College Dictionary" AHCD:

"1. A violent windstorm, frequently accompanied by rain, snow, or hail."
"2. Furious agitation, commotion, or tumult; an uproar."

In the non-wingers defense, windstorms do not necessarily descend from the sky; they can sweep across the land. Such a descriptor has been used many a time to describe the actions of invading forces, and it's not difficult to see how the second definition fits with marauding balrogs.

In the wingers defense, Tolkien himself did use the same descriptor to narrate the actions of marauding FLYING dragons. It is reasonable to assume that the author followed set, personal patterns for the telling of certain situations.

However, the chance that the meanings of English words as defined by the current edition of the AHCD held exactly the same meaning to Tolkien is highly unlikely. And as for assuming that Tolkien reused certain literary techniques, well, we all know what can happen when one assumes... :)

The falling-down-the-chasm scenario is also moot. There's just not enough there to gather any indication of the balrog's physical construct. We're talking about two supernatural beings locked in battle as they fall. Since Tolkien never reveals the full powers and capabilities of either Gandalf or the balrog, we can only speculate about the events of their descent.

As for debating how a balrog could manage flight by using actual laws of physics...what's the point? Balrogs aren't real. They're imaginary creatures with supernatural powers. Tolkien could have given them the wings
of chickens if he wanted to and still made them able to fly. Besides, science says that bumblees shouldn't be able to fly with the wings they have, but they do.