Take the MSF course.
I rode for a relatively short time (1 year), took a couple years off, then got another bike last summer. I took the course, and like you thought I'd be bored because I already knew how to ride.
They do start off as basic as you get, but once you start doing the riding drills, it's actually pretty fun. And you WILL learn new things that could save your a$$. Don't skimp on investing in protecting yourself.
I read some statistic about motorcycle fatalities in NH from last year. This may not be down to the right number...but out of something like 29 deaths, 20 were riders over 40, and only 2 out of the 29 were MSF trained. The point was a lot of people are getting back into riding today, that haven't ridden in a while, and because they don't feel like "beginners," they're buying powerful bikes and not taking the course.
The Ninja 500 isn't a bad bike at all. Thing will easily cruise at 100mph, and if you find one used, you should easily be able to resell it for close to, if not what you paid. Not to mention they're fun as hell for conering. If you have to go 600, the SV is the better choice out of what you have listed.