I snapped my boas 3 times in less than 2 months...then I just didn't replace it again and bought regular boots...never again. Granted I was racing boardercross at the time and was absolutely cranking the boots down...but either way, it's going break to sooner or later and not every shop carries the replacements.
My nike boots do not loosen at all...at least not a noticeable amount with an entire day of riding, and I'm willing to bet I ride a lot harder than most people on this forum. Nike has a system that locks down the laces at the ankle, locks it down at each eyelet above the ankle, then also has a strap that goes over everything...and of course you can always double knot it if you're really worried (I don't). I'm sure other boot makers have forms of this as well...you definitely shouldn't have to worry about your boots loosening up ever, I know I don't. And don't think that those boas can't get loose, all it takes is a slight bump to unlock that ratchet.