the point of having a big bankroll is to prevent from going bust. even the best players can go on 100BB losing streaks. and if you're killing those 0.25/0.50 games i hope you've moved up by now.
Why move up, though? I've found a niche that is banking me a very comfrotable amount of cash. I COULD risk more money, but in the limit I'm currently playing, I minimize my losses while maximizing gains by playing against the fishiest of fish.