Is Polonius a lovable but garrulous old man; a scheming and manipulating old pimp; or a pathetic old fool trying to survive as best as he can among far better educated and far more sophisticated people?
Readers, of course, can form their own opinions, but Polonius is clearly not averse to scheming. Indeed, he even sends his servant to spy on his own son, Laertes, who is at school in France. This in many ways is a harbinger of things to come. He arranges a meeting between his daughter and Hamlet, and then spies on the pair, hoping to discern whether Hamlet's madness stems from his unrequited love for Ophelia. (It is worth noting that Ophelia is under orders not to return Hamlet's love, putting her in a tragically awful situation.) Later, Polonius hides behind a curtain as Hamlet confronts Gertrude, a scheme which results in his death. Polonius, in many ways, is a typical court official, one who relishes engaging in the endless palace intrigues that so affront Hamlet. Notably he, like Gertrude, seems to have no reservations about Claudius as a ruler, and serves him as loyally as he did his predecessor. On the other hand, Polonius could equally be interpreted as a busybody, a sort of buffoon who, given his prediection for giving ridiculously bombastic speeches, is intended to be more of a comic figure than a malevolent one.
I guess I shouldn't answer my own question, but just to throw in my own $1.98 worth, I tend to resist the interpretation of Polonius as a scheming manipulator only because I don't credit him with that kind of intelligence. I'm not a Shakespearean, but Polonius seems to be partially inspired or derived from the stereotype of the meddling father in Roman comedy--which would place him somewhere between an annoying meddler and (as you say) a buffoon.
However, lately I have started to wonder just how comic or laughable he really is, given some of the very real and tragic consequences of his "meddling" and so-called "advice." He is a difficult character to read, in my opinion.