Late to the good-byes, but thanks for sticking it out as long as you did. I really like super-heroes, but I'd agree it's harder to maintain momentum with them. I think part of that is probably because, unlike a lot of other genres (traditional sword and sorcery, post-apocalyptic settings), four-color supers are almost exclusively part of visual mediums: There's lots of comics and movies with super-heroes, but (aside from the occasional tie-in) very little in the way of prose versions. So I think it's extra challenging to make PbP prose 'feel' like a four-color comic or summer blockbuster or what have you.
At least, that's my theory.