I do think it's important to make a distinction between a vendor's professional and personal "space."
For instance, if my FLGS began putting up political signage in the window with which I disagreed, I'd probably consider going elsewhere. On the other hand, if the store owner expressed the same beliefs on a personal blog, or while in casual conversation with someone that I happened to overhear, it wouldn't influence my buying. Similarly, I read lots of books by authors whose politics I utterly disagree with; so long as those politics don't infuse the writing, it has no bearing on my willingness to buy the books.
(Obviously, there are certain extreme beliefs that would inspire me to cease frequenting an establishment or buying a particular author, no matter where/how they were revealed. But these go beyond what I'd consider standard "political differences.")
I think you draw a good distinction between the professional and personal. It's not something that has to be absolute, and perhaps there's something that a shopkeeper feels so passionate about that he has to make it known to his patrons, but the reality is that, no matter what the issue is, if it's political it will probably cost you customers. Now, if it happens to agree with the political climate of the community (which is the case regarding my LGS) it may encourage more business than it discourages... but that's actually a tough call. I think it's probably more likely that something that someone finds disagreeable will prompt them to spend
less money on a luxury than something that they find agreeable will prompt them to spend more money on it... especially since they're probably already spending about as much as they want / are able to spend, given that we're talking luxuries.
-----
"This guy is for the vile proposition P. He should be for Q instead! Guess I'll save my money."
(seems more likely than)
"This guy is for the proposition P. Thank goodness he's not for the vile proposition Q. Guess I'll spend more money than I otherwise would have."
-----
It seems rather that, in the case of agreement, the patron will likely spend no more than he would have already spent (unlike the case of some sales and discount programs, where some patrons will actually spend more). But in the case of disagreement, they will spend less.
If that's true, then if the patron disagrees he will either spend what he would have spent, or spend less... but never more. And if the patron agrees he will probably still spend what he would have spent, because what he would have spend is probably the maximum amount to be allocated to that luxury expense.
Therefore my educated guess is that fiscally a patron only stands to lose when posting politicized affiliations; I'm curious whether the poll will shed any light on this.