AFAIK, in the initial encounter, the Borg were much more interested in technology than people. They really were something alien, ruthless, invulnerable, opposed to almost anything the Federation stood for.
Then with BOBW, they became able to assimilate people, and they changed, becoming more reliant on people (even if they were used as drone cannon fodder) and their knowledge than technology.
I once devised an original (or crackpot, take your pick ) theory, according to which the Borg were, actually, a super organism. The Collective would be a whole individual, while a single drone would be nothing more than a cell of this individual. Assimilating would then be akin to eating or breathing to the Collective, and the Collective's mind itself would be no more aware of the interactions between the drones and other lifeforms than a humanoid is aware of the action of antibodies against virii or gastric acids on food.
A whole civilisation would appear to the Collective as a mindless animal (because devoid of a mind in the Borg sense), ready to be eaten.
Based on that, there could be different Collectives - just as there are different individuals - each with their own specificities : some are "vegetarian" Collectives (they only consume uninhabited planets), some have weaker or stronger immune systems (Cubes...), and so on.
So everything the Borg have been seen doing in the various series would only actually be akin to the digestion or immune system of a super organism, whose true mind is so alien and evolved that its motives can't be fathomed by a single individual. And this would (partly) explain why there are stupider Borgs than others.
Mmmh... maybe I wasn't feeling very right when I devised that theory
Anyway, the trouble with the Borg is one encountered by any writer who wants to face the heroes with a truly powerful ennemy : if they make him too strong, then the heroes can't realistically beat him, but if he isn't strong enough, then he loses his "special übervillain" status.