As I said before: You should know what you need, then its really not that much of a problem. For most popular addons looking at the last page of a thread is quite sufficient to see if it still works on current versions of vB4. If, of course, you have no idea what the needs of the site are, then this will lead nowhere. But you really should not install addons for the sake of it.

I've determined it will be easier to go with vB5 and develop any necessary plugins from scratch rather than attempt to decipher which vB4 plugins might meet this client's needs. I can tell you one necessity is fully functioning social media connectivity. That appears to be problematic regardless of software choice or version.