If I were you I would shop around for the best price. Often there are cheaper offers off the main website but be careful, don't buy from unofficial sources.
Auto-renewal is at whatever the regular price is, but often you can get a discount elsewhere. If you go that route uninstall the old one in the normal way, run the MCPR cleanup (listed under Useful Links at the top of this page), reboot and then install your new one.
The about-to-be-released version of SecurityCenter is only slightly different from the current one and will be v12.1, some cosmetic changes, a new engine, and a couple of extra tools, depending on which suite you purchase.