I generally buy tires from the Motorcycle Super Store ... they do some pretty good sales several times a year. I typically buy a set for the Wing and a set for whatever else I ride over 7K / year. Now, it's my 2010 Connie. I have a set about 6 months old for the Connie, now. Wing coming after 1st of the year.
I never like to ride my sneakers until they are toast. I have enough problems riding other than worrying about my boots. So, I change them out about once a year or so. Most last me 7500-9000 miles. Give or take.
I've never worried about storing the tires. Yeah, I know all about the garbage bags, nitrogen infused stuff, controlled temperatures and humidity, no sunlight and such. But, I don't worry that much.
I've stored many tires for a year or so ... not longer cuz I only buy what I'll ride on in a few months or so. But, think about it. We have cars that sit outside ... in the sunlight ... in temps from -5 to +100* (F) ... in the O3 stuff ... under inflated half the time. Do we change them out? I don't. I run 'em until I need new rubber .. but, never compromising traction or safety. Sometimes 3 years or so.
My point ? I don't think we should buy several sets of tires in order to save $30 a set, or whatever. New models come out every year or so. Most better than what we have on our bikes ... or in the garbage bags. Buy on sale, buy when you need them .... buy Online where there is no sales tax (so far) and less than at the dealer. Yeah, I have the dealer install 'em. I gladly pay, too, for the installation. Some can mount their own ... I can't, or don't want to.
Just my opinion. Others will vary.