Thoughts on the Valar...
They seem to have taken a back seat in the events of Middle-earth. Which is fine. Things tended not to work out as well as they would have liked when they did interfere with the lives of Men and Elves. Numenor, while it started well, became problematic and was destroyed cataclysmically.
And too, I can see them being hesitant to intervene in anything directly. They didn't know the whole of the music, so they couldn't have been sure of Eru's plans. And where Men were involved, those plans had a way of being unpredictable, since the music wasn't 'fate' to the mortals. They left the business of running Middle-earth to its inhabitants, though they did what they could to help indirectly. Consider the Istari, sent to aid the free people against Sauron but expressly forbidden to use their powers to interfere directly.
A final point - who's to say that the Valar could have destroyed it? They weren't incorruptible. Melkor certainly wasn't. Gandalf feared the Ring. Saruman sought it for himself. If it went to Valinor, who's to say that one of the Valar wouldn't have fallen to it and become the worst Dark Lord of them all since Morgoth? Accepting the Ring could well have been the worst possible step for the safety of Middle-earth.
EDIT: Now, don't go and underestimate those magpies, master Pirateomer. Dread creatures they are, and would be quite good scouts for anyone. As for turning them to the good side, I suppose Radagast might have done so, but being that he looked every bit the scarecrow (at least to my imagination), I don't know how much help he would have been.
