It is tempting, I know, but don’t update until you have to.
Every update has some improvements, but every update also comes with a risk.
No matter how much time the developers (WordPress, WordPress theme, PHP, Shopp, or any plugin) spend on testing their software, there is always a chance some scenarios have been overlooked. When your site fits one of those scenarios… you are not going to be happy.
Every WordPress website leans heavily on more than a few systems that should work together in harmony. Unfortunately those systems are developed by different people. People with different thoughts, different ways to go about things. The more different elements you use, the higher the risk something is going to interfere with something else.
So if your shop is working fine, leave it. Don’t touch a thing until you need something new.
You want to change something
Before you start working on things, backup your files and your database. If things go wrong you need those to restore things the way they were. It would be even better if you could create a testwebsite, find out how things work before you implement it on the real thing.
Try to change one thing at a time. Test it thoroughly before you move on to the next change.