If only market share changed and nothing else, I would still use Macs and the Mac OS. I'd even like to think that the bigger profit margins for Apple would make Macs more inexpensive.
But truth be told, nearly everything I can think of loses something special -- usually the thing that made it worthwhile -- when it goes "mainstream." For easy comparison, I'd point to the time when the alt.rock and grunge fads hit, and all the people started listening to the bands I'd been listening to for years. You suddenly get a whole bunch of folks who are clueless about what they're using/listening to/wearing; they're only doing it because they cling to the socially accepted. And that inevitably takes its toll on the product or art, which, along with being hijacked by equally clueless business types, also naturally tries to preserve its dominance and ends up catering to these flavor du jour monkeys.
I *like* the niche. Not because it makes me feel superior, but because I don't need my peer group to approve my personal decisions, and furthermore, the niche demographic that's using the item has made a deliberate and usually informed decision to do so. Imagine a time when you ask someone why they use a Mac, and they don't start listing the advantages of the hardware/software integration or the elegant simplicity of OS X. Instead they just shrug and say, "Uh, I dunno. It was on sale." Won't you say something about the whole Mac experience will have gone missing?
And even Apple would fall a victim to crowd-pleasing. Just look at this iPhone and Leopard nonsense, for instance. The longtime Mac user base has become a second priority, and the next OS is delayed because of some silly fad product. But just think of all those high schoolers (with all their parents' purchasing power) who will be upset if it's not out by June!
