I guess you really need to define "upgrade" in your mind. There are gives and takes with any change. More balls=less MPG. Smaller=what are you gaining? Do you commute or do you play? If I had a 500 and was willing to keep it for the commute, I would get something different, if not opposite. A second bike could be a gas burner, a sportbike, a DS, a cruiser .... define your true intentions and the sky is your limit (up to $3500).