Actually, there are two ways to subscribe, now.
1. The yearly subscription, one payment of $29.99 and
2. Object Desktop Infinite. That plan sells for $9.99 to start and then $3.99 per month thereafter. You, as a return subscriber might not have to pay the initial $9.99. Since I'm just another member, I'd verify that with Stardock sales. Clearly, the $29.99 choice would be the lesser sum. You can read more about that here: http://forums.wincustomize.com/458719/page/1/#replies
As for updates, being current in either plan would assure you of all the updates, whereas allowing your subscription to lapse would exclude you from updates, but not the use of the apps. As Wizard1956 pointed out, "Your software can be activated with your key without an active subscription.", but you should download the latest version of your installer before your subscription lapses (if you decide to go that way), save them and back them up, but realize that Stardock is free to change that policy at any time without warning.