Yes it is. :)

: Firstly, and most obviously, the Balrog in Moria made no
: attempt to keep itself in the air after Gandalf broke the
: Bridge at its feet. (Although we could get round this one if we
: had to. Even birds will fall if knocked off their perch
: completely by surprise, and the Balrog does appear to have been
: taken by surprise. Then, in the confines of the fall in the
: chasm, perhaps it did not have room to properly spread its
: wings).

There is no need to "get around" this objection at all.

The Balrog's wings spread from wall to wall in the immense cavern. As you suggest, flying should have been an impracticality in the chasm. However, Gandalf said they fell a long time, and even though the Dwarves had never measured the depths of the chasm it is highly probable that the Balrog floated down to the water as Gandalf hacked at it and it burned him with its flame.

: Significant also are the records of the Wars of Beleriand.
: There is no suggestion anywhere of Balrogs launching aerial
: assaults....

Incorrect. They flew over Hithlum to reach Lammoth and help Morgoth against Ungoliant.

: For example, in the Fourth Battle, Dagor Bragollach, the
: Balrogs came out in the train of Glaurung - i.e. behind him, on
: the ground.

Nope. "in the train" does NOT mean strictly on the ground. It only means BEHIND him.

: Likewise Gondolin was clearly attacked from the ground, not the
: air.

[snip]

Bad example. The only full account of the fall of Gondolin was written in 1917, decades before Tolkien changed the Balrogs into corrupted Maiar who took on flying winged shapes. Christopher CONDENSED the older story rather than rewriting it.

: On balance I think we can conclude that Balrogs did have wings,
: as such they may have been able to glide over short distances,
: but they were definately incapable of sustained flight.

The evidence indicates quite the contrary. The Balrogs flew to Lammoth from Angband. That's a very long distance.

: Did they speak? They must have been able to. As Morgoth's chief
: lieutenants and commanders of his army, they must have
: been capable of giving orders to the Orcs and other creatures.

The Balrog of Moria spoke. He uttered some profanity which Gandalf dropped the mountain on him. :)

Most likely, however, the "counter-spell" that Gandalf detected involved speech. Magic in Middle-earth seems to be closely tied to song and speech.

: The Book of Lost Tales (which, while hardly canonical, does
: give some guide to Tolkien's thinking) does record Balrogs
: speaking.

[snip]

Again, for the reason given above, THE BOOK OF LOST TALES is not a source of information on LOTR-era Balrogs.

: The Balrog in Moria never says anything, probably because it
: did not speak Westron.

[snip]

It cries out when it falls into the chasm. It could have been cursing in Valinorean or merely giving out some primal scream.

Good points, nonetheless, about the Balrog's long sleep and Shelob versus other giant spiders.

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The Lord of the Rings and Balrog Wings, Oh My!