I realize that. However, that audience would be a foundation. It's not like all Trek fans read the novels. Not only that, but if properly done, I believe such an adaptation could reach a general audience and be as successful or even more successful than a Prime universe movie like First Contact. Just to clarify, I mean the individual films of the trilogy by themselves would be that successful.
Who knows? Speaking for myself, though, I'd have absolutely no interest in seeing such a film. I think while it may make for a nice reading for fans, it would be the wrong direction for the franchise and would probably lead to a rather unsatisfying cinematic experience.