I can think of several other reasons to leave one's solar system: Sport/competition/personal accomplishment and scientific or cultural curiousity leap to mind.

I don't recall reading or even hearing of Hogan's Trilogy, but I'm sure I stole that phrase from somewhere, rather than thinking of it myself.

Although I see carnovorism as offering certain evolutionary efficiencies in accreting sufficient high quality nutrition, I've also thought that predators and prey seem to expend an awful lot of energy running around chasing and evading that could otherwise be used for more productive pursuits, and wondered if perhaps nature could have found another way to create evolutionary pressure.

Jeff