I bought a Ninja 500 for my fiance to learn on.
I was simply amazed at how nice of a bike it is, and have been riding it much mor than my Concours.
It feels like a 250 below 6000 RPM, but then has a midrange and upper end rush that leaves you feeling like it'a an older 600 class bike.
It is rock stable on the highway, and the fairing actually works pretty well. Handling is very good and made me realize how poor the Concours is in comparison.
I plan on having something like this, a 400Lb twin, from now on, and will probably upgrade to a 650R when the used prices come down on them. That bike fit me better than any other I've tryed out, but it outside of my budget range at this time.
Upgrades I have made or am in the proces of doing, are tubular bars for a more upright position, frame sliders, straight weight fork springs of the right rate for my weight, and a shock upgrade of some sort, again, to match my weight.
Keep in mind that you'll get bored with any bike, if your attitude is that you will get bored with it.
I rode a 250 for 4 years as my first bike and never got bored with it, but that's back when the speed limit was 55. I wanted more power, but it was never boring. I feel, with today's higher speed limits, that the Ninja 500 is about the same type of bike now, one that will give you everything you need, if not everything you want.