I love this Newgrounds+ idea. As long as disabling the scripts I don't want will completely turn them off as if I disabled them in Tools > Extensions (so that they don't use up CPU power) then I think it would be great to have it all in one script.
Suggestion: Is it possible to make the notifications button notify you of different things other than just new content from your favourite users? Stuff like new reviews on your submissions, new replies to your forum posts, new comments on your newsposts, new users who added you to their favourite artists list, etc...? This is the one thing I want there to be in the redesign the most but the NG staff don't seem to be implementing it any time soon.
If you do implement the above, though, I'd highly suggest making it so that it calculates these notifications when the user presses the notifications button (not like, for example, in Facebook, where the notifications are updated in realtime), because I'd imagine that searching for new reviews/replies/etc would take a bit of time and processing.