[Legate of Amon Lanc]

I absolutely agree with Bêthberry here. Tolkien's strength is not in surprising ending or a twist in the plot (the thing which is almost essential for a good novel), even the final revelation that the Shire is destroyed and that Sharkey is Saruman is not, in my opinon, that surprising twist, though it has very close to it.
As I said in the Foreword thread, I did not read the Prologue the first time I read FotR, yet it did not bother me in the slightest: I did not seem to miss anything (like knowing when old Toby started to grow his herbs) and, of course, I was not affected by the spoilers - at least in the beginning. Nevertheless, it was quite clear to me that Frodo survives and I must say in Cirith Ungol I did not think for a second that he could be really dead, and I'm sure any spoilers would not play any role in this, whether I read them or not.

Originally Posted by Bêthberry

So it didn't matter if readers guessed from the Prologue that Frodo survives: the interest was in his internal journey and how he came to survive.

Only to this: at least personally, my interest was not during my first reading - and probably not even in the later readings - whether Frodo or how Frodo survives at all. In fact, Frodo and the hobbits were on the edge of my interest. I could even say that it was not that I would follow the tale of Frodo and the Fellowship, as they pass through some sceneries and events and pass by some people, but that I was trying to explore all of Middle-Earth's sceneries and events and characters, while I had some group of Frodos to lead me through, like tour guides. You know what I mean? At least for the first time, I hardly cared about Frodo or his mission, even. I entered this fantastic world and the only way I could explore all its beautiful places was to follow the "camera view" that was given to me by the author. Otherwise, the world was shut to me, it was a different world that I was not welcome in, that I did not belong to, but as long as I followed this group of Frodos and Sams and Striders, I had the privilege to take a peek at least on a little part of it. (And after all this time, today I can say that only very slowly it has opened to me, but I can feel a little more welcome in there and I feel I can move almost freely there now.)
It's not that I would completely ignore Frodo's quest and the storyline: of course not, I was thrilled at many moments, I was moved, I shared his or his fellows' feelings. But it was not the first place for me, and only in later readings this gained more and more importance for me.