You did!
[spoilers="District 9"]The movie explained that the aliens we saw were low-level workers, and that their "leadership" had died off. The implication is that they use some kind of caste system, with a large gap between the various members of the species. They possess raw intelligence, but the idea is that they've basically just been manual laborers or engineers their entire lives. They're also, of course, very desperate and run-down by the time we see them.
I'll agree, however, that it might have stretched this point just a little bit at times. I buy the explanation, though perhaps not to enough of a degree to account for everything we see on screen.[/spoilers]
[spoilers="District 9"]Well, there's a big difference between a plot hole, and something which is deliberately unexplained. The aliens running out of fuel is not a plot hole, it's just something we're not told about. For all we know there was a leak, or a technical malfunction. There are plenty of possible explanations.
As for the weapons: I think that, too, is explained by their leadership dying off. By the time the humans actually fly up there and break into the ship they're already starving and trapped without adequate power, and obviously the weapons are mostly confiscated. Some are floating around on the black market, but not enough for some kind of mass uprising, obviously.[/spoilers]