The thing that derails that film for me was the whole inner/outer planets thing.
Didn't Whedon backpeddle furiously on that one (after his plaintive "science is hard!" statement
). There were uh lots of terraformed space stations, asteroids and whatnot.
I have the same problem with the modern (Star Trek III and later) Klingons that you have with the Reavers: I don't believe for a moment that these people are capable of inventing the light bulb, much less achieving any ongoing technological culture over periods of centuries, because they're just too stupid and violent.
Eh? Modern Klingons have been depicted as being boisterous and sometimes looney but overall I can see them having a coherent, successful spacefaring society. They are smart, aggressive, creative, adaptable, insanely courageous and occasionally over the top but not self-destructive. They have their places in society and it takes a lot to get one of them to dishonor themselves by stepping out of the bounds.
They derive their social order from that "honor" shit they keep nattering on about to everyone's annoyance. There's a reason they make a fetish out of honor the way Vulcans make a fetish out of logic - those are both elements their respective cultures use to keep from imploding.
Of the two, I think the Vulcans are the ones with the more endangered culture. Their emotions are more violent than humans and made it extremely difficult for them to cohere as a society. So the Vulcans came up with one adaptation to their inborn handicap. The Romulans presumably came up with another adaptation (extreme xenophobia and its mirror image, extreme loyalty within the group - I can't think of what else it might have been).
Romulans and Vulcans have it much harder than Klingons. Humans have it very easy. That's probably why everyone is always hostile to humans - spoiled brats!