How important is that to you, really???
Not being able to get your "odd ball" ammo at every mom & pop country store, or at WalMart??
That would be quite important to me, since firearms are not just a recreational tool, but a survival implement. When you need to use it the most, and you cannot find ammunition for it, it would just become a glorified paperwork.
If I were to get a semi-auto handgun right now with more tactical features and increased magazine capacity, I would choose between .45 ACP or 9mm. Even .40 S&W would behind the main choices, as the first two are the most commonly available calibers. I definitely would not be considering 10mm, .357 Sig or 5.7x28. I would rent them at a range just to have fun, but as an investment, I would only go with most common calibers that are also used by law enforcement/military.