Thanks DCindexer, I can pretty much infer all the answers to my questions from the article you attached. I knew comics included the mandatory prose pages pretty much from the beginning. The most famous one of all was May 1941's prose story in Captain America #3, Stan Lee's first published work in comics

Letter pages most definitely were counted as prose pages and wound up as (obviously) superior substitutes to those fiction pieces that nobody read. I'd imagine the Marvel Bullpen pages counted as well 

Marvel had some great letter page regulars and thanks in large part to their help the letter page was a highlight of the reading experience every issue for some series - ToD, MoKF, and most of the Gerber books come to mind, just to name a few examples. Was the same true of the DC letter pages?

I remember that thread, but I probably skipped the DC parts because I wouldn't have recognised any names, apart from future pros like Martin Pasko, or known what they were talking about. But good idea, I'll look for it again.

One prose page I remember liking was Jack Kirby's occasional little essays where he's talk about the ideas behind a series such as the Eternals, usually in the first issue , before there were any letters to print. I think this would have been a good thing to do on a semi-regular basis, except I suppose I wouldn't want them to take away another story page, especially in the 70s when they were already down to a measly 17 pages. But I would love to have read occasional essays by writers like Englehart, Gerber, Starlin, etc, commenting on what they were doing in their stories. Of course we did get a bit of that in the letters pages, in their responses to the LoCs, but it was very brief and piecemeal.