I have a Ninja 250 as my city/sometimes commute bike right now and think the CB500 in F or X trim would be a good step up for what I use the Ninja for. I don't care so much about the power difference, but the Ninja is just too small for me size wise and if I can average 55mpg with the Honda I'm sold on it.
My daily commuter is a nekkid Bandit 1200 with windscreen and Givi monokey luggage system.
-Jake