[Elrian]

The Maia like the Valar can take whatever shape they wish, I remember reading that many Maia remain in spirit form though. The Valar may have chose the shape of men for the Istari since the Elves were departing and the age of men was at hand. The Elves in the Third Age had little to do with Men,or other races, the exception being the Rivendell Elves.

But like someone said above the Hobbits were valiant in their own right, though the other races didn't know it until the War of the Ring. Or maybe the forgotten Battle of Fornost where it is said the Hobbits sent archers to aid in the battle.