[Pitchwife]

I don't think this scenario works (or not like you present it, anyway), for a number of reasons.

Originally Posted by Gorthaur

For I've never seen such powers (high magic) from both during the 2nd Age or the 1st.

This may, in part at least, be explicable by the facts that the Silmarillion, not to mention the sparse records of the 2nd Age that we have, is told in a much more remote perspective than LotR. If Tolkien had ever fleshed out the legends of the Elder Days in the same detail as LotR, who knows what we'd have seen?

Originally Posted by Gorthaur

The elves of Tol Sirion, for example, relied on Ulmo's power to defend them, yet if Elrond or some other high elf lord were there weilding Vilya, they could've been better protected without Ulmo's intervention.

1) We don't actually know that Elrond used Vilya to cause the flood at the Ford of Bruinen (for reasons why I don't think Vilya was involved there, see below*). The Nazgûl's general fear of flowing water (also testified by their reluctance to cross the Brandywine) suggests that Ulmo's power was still present in the streams in the 3rd Age, all Elrond had to do was to invoke it. If you wonder why it apparently was unusually easy for him to do this, consider he was the son of Eärendil and grandson of Tuor, to whom the Lord of the Waters had shown exceptional favour. No need for a Ring to explain this.
2) It's one thing to drown nine Nazgûl (not yet revealed at the height of their power), another to fend off an attack by a whole army of orcs led by your abominable namesake in person. At the Council, Elrond himself admitted that he had not the strength to withstand Sauron in a direct confrontation.

Originally Posted by Gorthaur

I could see Morgoth having a very hard time capturing Gondoling with Turgon weilding Vilya

He had a very hard time conquering it without that, and the odds are he would have succeeded, if at all, much later and at much greater cost without the treason of Maeglin. But what if there had been a traitor at Rivendell?

Originally Posted by Gorthaur

I could also see Finrod withstanding against Sauron in their duel if he had worn Narya, enhancing his still fresh-off-the-boat, two-tree-lit-aman-bred spiritual stature/power. Or if it hasn't come to that, I could see Nargothrond not falling against Glaurung if protected by Narya.

Considering that Narya's chief virtue seems to have been in enhancing willpower, I agree it might have aided Finrod in his confrontation with Sauron. But Nargothrond fell because Túrin, in his hybris or ofermod, refused to listen to Ulmo's counsel. Don't see how Narya could have changed that.

Originally Posted by Gorthaur

Take these suppositions with all the seven sons of Feanor dead, of course, so as to rest the curse of Mandos

This is a minor issue and unrelated to the question of the Rings, but as I understand it, it wasn't Feanor and his sons only who were under the curse, but all the Noldor who had rebelled against the Valar and taken part in the first Kinslaying.

*Vilya was the Ring of Air, Nenya the Ring of Water. If any of the Three gave its wielder special power over water, it would have been Nenya, not Vilya.
But this leads me to another question. This thread, and the one about Nenya and the Elessar, have made me think a bit about the specific virtues of the Three, in other words the nature of the power each of them conferred on its wielder.
Each of the three is named after one of three elements - Air, Water, and Fire; at first glance, this looks like they gave their wielders power over the respective elements. Now Gandalf, who had Narya, certainly showed exceptional skill in the handling of fire (fireworks, naur an edraith ammen, wielder of the Flame of Anor etc.), but being an incarnate Maiar, he certainly didn't depend on a Ring for this; as for Elrond and Galadriel, I don't see them controlling Air and Water in any obvious way. So what does it mean?
In esoteric thought, the four elements are associated with different faculties of the human mind/soul. Applying these associations to the Three Rings, we get:
Vilya - Air - reason. The chief role of Elrond in LotR and The Hobbit (apart from his being a great healer) is offering counsel, giving advice to others based on his wisdom and knowledge.
Narya - Fire - will and passion. This is the most obvious correspondance: Círdan gave Narya to Gandalf 'for the kindling of all hearts with courage', to strengthen their hope and determination to oppose Sauron.
Nenya - Water - emotion, intuition, the subconscious. This is the least obvious, but (to me at least) it somehow resonates with Galadriel's love and yearning for timeless beauty, as well as the scrying power of her mirror.
I'm not saying any of this was on Tolkien's conscious mind, but it seems to fit, and it may be worth considering if we speculate what use 1st age elves might have made of the Three.

(x-ed with Gorthaur's last, which I don't consider here, or I'd never get this posted)