I'm of the school that a reasonable amount of buildup = flavor. Once I get chunks in the corners, then I'll break out the brush. Your flare ups will come from the flavor bars, so you want to make sure you get any major buildup off those. Be gentle, those things rot out after a few years.
One thing about the Genesis you should know is that you need to take care aligning the bottom sliding part. The hole will always hit the drip tray, but if you leave the slightest opening in the front or back of that sliding piece, you'll get drippings on your deck or patio.