I paid £80 for that upgrade and thought it was worth it, but I agree with Anthony. You can install 4 and run it alongside 3 but you need to know that 4 will upgrade your catalog and 3 will no longer be able to read it. So try 4 with a new, temporary catalog until you're ready to upgrade then, after the upgrade, back up your catalog and then open it in 4 and allow it to convert it. Or them, if you use multiple catalogs.