Are there any advantages to V5 to make it worth upgrading?

The main disadvantage - if you don't upgrade - seems to be that if you need support, you won't get support for an old version. Also, the users here in the forum will have upgraded and won't be able to help, if you need help. If one of us makes a file with some example, you won't be able to open such a file because of version conflicts.
If you want to use components or templates, they are also mainly made with newer SD versions.
Of course, a new version will always have something new in them, and some fixes for this and that, but off the top of my head, I don't remember which features came with version 5. Well, certainly the 'Opening' of the Component shop happened after version 5 had appeared. For other highlights, you could read through the changelogs to find out.

I would also say that it depends on how often you would use it. For the occasional use then probably not worth it, for regular use then definitely essential.