I started using Unity a couple of years ago, before vvvv.
It definitely is nice and got improved a lot over the years.
I must agree with m4d that vvvv is unbeatable in rapid prototyping.
I think Unity really has its advantages in the more realistic 3D world. It is really easy to import 3D models - setup animations etc. Doing abstract stuff like in vvvv might be hard in Unity (spreads are really neat). Also Unity is mainly used for Game development (not exclusively).
I think the disadvantage of visual programming is that (in case you dont write your own addons) your programming skills are not improved, maybe logically - but you really dont learn c# or similar.