I like that better than "type of Christ". When I first began reading LotR, I felt there was something- Christ related with Gandalf, but not exactly a representation of Him, as I went on, and he would show up to encourage, inform or suggest after a course of action has begun or was getting bogged down, that kind of made me think he was more like the fundtion the Holy Spirit in my life.
It did occur to me that it might be similar to one of the Archangels- whereas only Lucifer fell to become Satan taking some angels with him- comp: Sauron/Sarumon's rebellion and the Orcs (corrupted Elves)
The other two Michael and Gabriel remained loyal.
I think you are right, that this is NOT an allegory, but it is interesting that he uses so many Christian tenets, and illustrations-
RE: Fire, Tolkien sure does use it in a lot of ways. Don't forget the the fire of the forge, both dwarf and elven- to strengthen and sharpen- The Balrog- to burn out impurities? remeber that Gwaihir said that Gandalf was light as a feather- and that the sun could see through him after his experience with the Balrog's fire. "I was burnt."
Sorry, I need a nap, getting rambling here.