I took my MSF course on a Ninja 250 and it was very similar to the honda. They are both great bikes and forgiving. I went back to the course with my CBR and the drills were still difficult about two months later. One thing that I noticed with my honda when I first rode her is she doesn't like taking off at lower revs and bogs down. I don't remember that being an issue with the Ninja and it was only a week later that I drove my cbr home.
As for the fun issue, the only thing I sometimes want a faster bike for is accelerating on the freeway after I'm at speed. Up to around 70 MPH this thing is quick enough that I can overtake and do what I want. I have been riding for three months now and 7,100 miles and the bike never fails to impress. As I get better it gets better. Truly I can't imagine outgrowing it any time soon. I think once I'm out-cornering 600's at the track then it might be time to upgrade. Right now, I still get scared in some corner's.
Riding a 250 requires you to check your ego. Everyone, even non riders, has something to say about it being a 250. It is really funny, but only I know the joke as many hobble off on bikes they can't handle and are afraid of. Most haven't even heard of the techniques I have learned. I credit the bike and my willingness to learn in a safe way. I still want a 600 so they will shut up, but it would only be useful in making up for slow turns and wearing out tires quickly.