Weren't there a *spoon* Tracy Feature book and a Dumbo paint book that were also pretty hot items? Mickey Mouse Outwits the Phantom Blot is still on my want list, too, but I might be one of the last collectors alive who is still a fan of that book. I never hear it mentioned.
Cap #1 might be an important book, but it's pretty common compared to Batman #1 and Supes #1, isn't it? So it's hard to see it eclipsing those in value any time soon.
Also, Captain America seems to have the same image problem that Superman does: he's a bit too much of a goody-goody. Younger collectors seem to be more into Batman, Spider-Man, Deadpool, Wolverine . . . edgier characters, so I really don't know what Cap's prospects are over the long haul. Time will tell, I guess.