Greg - I do open mics for fun, but I agree that there are things I just won't haul my stuff out of my house for, e.g., country, modern rock, blues ... and by that I mean three, four sets of the stuff.
If gas money is covered, I'm usually good with most things, however. I'm not a professional musician (though when I do play I try to adhere to professional standards), so it's not like I'm going to starve if I don't make dollar X for each gig. It's when people expect you to pay for free (oh, you'll get great exposure! - look, if I want exposure, I'll lie out in the sun) that puts me off. It costs money to buy the instruments, amps, other equipment, a vehicle to haul it all in, gas, insurance, etc. Exposure doesn't pay for any of that. Now, if you're doing a benefit for something out of the kindness of your heart, that's one thing. But playing for free? There has to be some modicum of remuneration if you ask me.
And I'd agree also that I'd rather play out once a month or so where folks would appreciate the music. Nothing like playing for folks who dig what you do (or don't do).