There are lots you can do to make sidewalls look better including lacquer thinner like the used car lots used to do.
I would defiently not advise doing that! Laquer thinner will dissolve the rubber compunds, making the tire weaker. It'll make it look better for sure, but it isn't good for it.
Also, take care using Armor All or other tire "protectants". Overuse can cause degradation as well.
The best thing you can do to extend to life is to store them in a cool, dry location away from UV rays, preferably inside a garage. Keeping them off the ground will help, too, by preventing flat spots, especially with bias ply tires.
