The 600 makes a perfectly good track day bike as is. If you crash it, then you suffer the consequences with your everyday ride. I'm in a club that hosts track days three times a year for our members and one of the tracks we ride is Talladega Gran Prix Raceway where at that time the track record was 1:01 and we had a physician riding a stock Bandit 600 turning 1:09's. For a reference, my best was a couple of 1:21's on my Bandit750. If you want to run the 600 at track days, I would suggest a few things: don't overtire the Bandit. Run stock sizes and don't go any softer than a Metz M1. Run stock pressures or at the most no lower than 30/32. A set of front springs and fresh fluid.
Maybe a cheap Progressive rear shock. Set your sag and have at it. Don't even spring for HH brake pads. My Bandit is 10 years old and I run track days several times a year.
Of course, you could go to the racer boards and pick up a F2 or gsxr600 cheap and do it that way. But for 2 or 3 times a year I wouldn't make a big splash on spending dollars. The 600 is a great bike.