Good deal on Nitto's ?
 

ebay is also running a sale. $50 off a set of tires bringing the total to $467.

I don't need tires at the moment, but I might scoop these up for future use. Is it wise to have tires sitting around for a year or 2?

No, they age and dry out.

Tires won't dry out in a year or two, especially if stored indoors, but fresher is better. I would just wait until you need them.

When I looked at stock Nitto 555's for my '99 SS 2 years ago they were around $115/tire w/o any discounts from my regional tire store. Had there been a discount available I just might have bought them.

If you figure the tires are good for 10 years (probably the longest any installer/dealer would stand by) that's about $46/yr in "age." At using the typical 6 year "dealer" life, it's $115/yr. So aging alone can be costly.