I'm happy with my copy of Dreamweaver 4...yep 4, got it cheap off Ebay. I say upgrade if you need to do something that only the new version can do. If you can do the work with what you have no need to spend the extra $200 IMO.
web standards are constantly evolving. Old versions of Dreamweaver write to old standards. Old Standards eventually become less and less supported. It's like insisting on using a dictionary filled with old english vocabulary because the book itself is still in good condition. You need to be using a program that supports current standards, whether it's open-source, free or commercial.