Last night I made a new post about features I thought were missing from Silver Efex (Contrast and Structure) I must have been having a 70 year old ‘senior’ moment 
The panels weren’t expanded. While I have your attention, what has really changed over the years apart from the new perspective module … I already have DXO Viewpoint 2. Being a pensioner I have to spend money wisely, is it worth spending A$137 on what really seems no different to what I had? I guess, only I can answer that.
I responded to your other post before I saw this one, glad you got that sorted. There are new film presets in Color Efex 4 and also in Silver Efex 2 I believe. There is also a non-destructive workflow option within each module that I have found to be extremely useful on numerous occasions. Also a new selector mode that is usable within Photoshop. But as you mention, only you can decide if these improvements are valuable to you.
If you can do what you like with what you’ve got, the answer is NO.
If you want to know what the new release does, download the trial. Make sure you have the installer of your preferred version to be able to fall back if you don’t like the new version.