For the most part, I wouldn't find poll results very useful in deliberations on site policy. I'm usually more interested in why you hate/love some idea than how many people "agree" with you. Poll results almost always have as much to do with rather minor quirks of how the poll choices were worded. In a real discussion, quirks in the initial wording can be addressed.

I initially thought PM polls wouldn't even support a useful question type (a yes/no poll would be pretty useless, IME), then I realized that a "hate it, dislike it, meh, eh, like it, love it" PM poll could be useful in some simple situations (though I still doubt such would be worth the time and effort in most cases especially since there is usually much more to consider at the same time). Having recently gone through a rather large number of "strongly agree ... strongly disagree" poll questions, I think I might prefer if responders could fill in a range when answering such questions (my response falls between "meh" and "like it").

Trying to turn PM policy matters into polls would require a whole series of polls as the issue evolves and most of the polls would end up being rather useless as by the time some aspect is boiled down to a simple issue that is well enough understood for a reasonable poll to be produced about it, there is a good chance that the point of interest has moved at least a little bit (which likely makes the poll answers that much harder to interpret).