[Lalaith]

I'd never thought about why the Ring made you invisible, that's a very well-thought out thesis, Maédhros.
One speculation - Gandalf, not an elf, wears one of the Three. He was born as pure spirit - his hroa is something assumed. The ring he wears clearly has no effect on his assumed hroa.
I've no idea if this point is in the slightest bit helpful to the discussion but there you go.