[Inziladun]

Originally Posted by denethorthefirst

Another thing that i find curious: Tolkien wrote that the Istari aged, albeit very slowly. When Saruman appeared in Lindon he had black hair but by the time of the War of the Ring it had gone completely white. If you take this development to its logical conclusion, doesn't that mean that the Istari would, eventually, "die" if they stayed long enough in Middle-Earth?

I don't have the books with me, but there was an observation that the Istari, though clothed in physical bodies, did not die because those bodies were "supported by the angelic spirit" of the bodies' inhabitants. The physical aging process was slowed, but not arrested.
So, I guess that does mean that the body would eventually completely wear out, but the Valar guessed that before that could occur, either Sauron wold be victorious and the Istari destroyed, the Istari would die by other means, or Sauron would be defeated.
I don't think Sauron himself necessarily knew the exact nature of the Istari, and it possibly took quite a long time for him to reach the assumption that they came from the West, maybe not until Gandalf's infiltration of Dol Guldur. Also, he might have also wondered about your next question about why a Maia in an earthly paradise would have come to Middle-earth, causing him more confusion as to their origin.

Originally Posted by denethorthefirst

Because of that, i never fully understood why those five Maiar undertook the mission at all. Why would an immortal, naturally discarnate being do such a thing? Become imprisoned in a relatively frail body with an expiration date and, essentially, go on a suicide mission that, if it fails, would spell certain "death"? For all eternity? The incarnation process at least seems irreversible? Or did the Valar promise the Istari that, after their victory over Sauron and their return to Valinor, they would reverse the incarnation and return them to their naturally discarnate state, able to change their "clothing" at will?

I am sure that after returning to Valinor, Gandalf was restored to his natural, unfettered state of incarnation. That was a given, for all the Istari upon their return.

As to why they went, the chapter The Istari in Unfinished Tales sketches a meeting of the Valar, in which they were deciding who would be sent. From that, I get the impression they were "voluntold" for the assignment, especially Gandalf.

But if they did go of free will, it was either a sense of duty, or a genuine concern for Middle-earth, or both.

Originally Posted by denethorthefirst

But, given all that, what exactly is Sarumans End-Game in Middle-Earth? ....Maybe he thought that, with the One Ring, he would be in a position to strengthen his body and have the power to prolong its life or maybe reincarnate himself in a completely new body? Thats the only explanation i have, otherwise Sarumans actions make absolutely NO SENSE in my opinion, just from a purely self-preservation perspective, disregarding the whole moral dilemma.

Saruman had become so blinded by an infatuation with power and overlordship that he wasn't thinking clearly. It seems that very early he began studying Sauron and his works, and, instead of using knowledge gained to formulate strategies aimed solely at his defeat, developed a sense of envy for Sauron's power and control. Finding the Ring became an obsession, and the only thing he really cared about.