I have a hard time seeing wizards as acrophobic. JKR seems to have established that they're much hardier than Muggles and more difficult to injure. Any phobia really isn't a fear of the thing itself, more a fear that the thing will cause serious pain and injury. A bludger to the skull would kill a Muggle, but merely knock out a wizard. Oliver Wood may have been out for a week, but suffered no lasting ill effects. A Muggle would likely have suffered brain damage.

Do I think Snape is "good enough" on a broom? Yes. It's the wizard equivalent of a motor vehicle. You're a wizard, you know how to fly a broom. I think as a pureblood, he'd be especially proud of his magical heritage and the uniquely magical legacy that is flying. As other peope have said, while he may not have gotten the hang of it so easily as a student, he's an adult now and likely has overcome whatever awkwardness he had as a teenager. You'll notice only teen!Snape moved like a spider. Adult!Snape moves like a bat.

Do I think Snape is any good at quidditch? I don't see him as particularly interested in sports, even a uniquely wizard sport like quidditch. Of course, most Americans are similarly proud of baseball or football (Canadians, hockey), but that doesn't mean all are athletically inclined or interested in actually playing (or attending). Do I think Snape can play? Yeah. Do I think he's any good? No. Passable at best, but passable only gets you on the team if Umbridge is in charge. :-P