Melda Productions has a dynamic EQ I've used and liked.
You asked about multi-band on a single track...
Applying top end compression and lift on a vocal is a pretty common single track vocal treatment these days. You can even bypass the other bands when you do it if you like. I'm only just giving an example.
Part of the idea behind a dynamic EQ from my perspective is that it emphasizes what you are up to.
I think the dynamic EQs are interesting b/c they emphasize how the EQ and compression/expansion go together. Sometimes you actually expand below a certain signal and compress above another level... this helps quiet the quiet times and quiet the loudest times while leaving the bulk of the track in place.
It can make a lot of sense to compress a track based on the frequencies that are overwhelming. It's a bit more surgical.
I'll be honest, I own the dynamic eq and I use it sparingly. I'm not hugely comfortable with it at this time.