The Norton Superlight (335 lbs with titanium exhaust) and the new Aprilia RS 660 appeal to a different riding mindset than the high HP sport bikes, regardless of potential pricing similarities.
I have an Aprilia Tuono Factory V4 and while it is a great bike, I often times have more fun riding my lighter bikes (MV Agusta Rivale and SWM Supermoto) on the street, regardless the fact that they have far less power. I'll keep my V4 Tuono though, as it's fun to have a high power bike to ride at times.
Most of my friends have multiple bikes and tend to have a variety of configurations. I have a single cylinder bike, a V-Twin, a Parallel Twin, a Triple, and a V4. Experiencing each bike's unique personality, handling characteristics, and power delivery is part of what I enjoy about riding. I like variety.
I think that the desire to ride lighter weight bikes on the street is not a new mindset, but one that I see growing among my riding friends.