Do you pay attention to how many buttons are on your shirt placket? Do you avoid shirts because of too many or too little buttons? Or you just don't care?
Yes, depending on spacing will avoid too few or too many on polos cuz the shirts don't look "right" to more or as nice... 3 seems to be the sweet spot IMO... 2 or 4 can work if spaced well... 5+ is often getting into crazy town. ;-)
2 or 3 is the permanent acceptable range (just like suit jackets). Fashion will push it back to 1 or up to 4 or 5, but those styles fade. I have a 4 button shirt right now, but it feels like too much. I kind of prefer 3 right now.
It's definitely something I notice, but not something I've given too much thought too. I normally notice it when I throw on a golf shirt that only has two button and I'm only closing one (I'm thinking Nike TW version of a year or so ago).