Screw the manual, aim it where you want the light. With a stock sealed beam I tend to shift it around quite a bit when riding. For city day/night driving it's mostly an attention-getter so cagers notice me, aimed pretty high. Putting around out of town at night I want it aimed low to show the ground directly ahead of me. Faster riding in the country at night I set the high beam to light the road ahead as far as it's effective; no point in wasting light into thin air.
H4 halogen lights and some halogen sealed beams have a very sharp cutoff on low beam, set it at the horizon with you on the bike. The high beam should be at its best angle this way too. I don't generally mess with the H4 like I do with the stock type sealed beam, except to tip it up slightly in rain to shine brighter at oncoming car drivers.
As far as bouncing goes, the pivot washers get hard or shrink or whatever over the years. There's a shoulder washer in there you can file down a little to tighten the clamp, or get/make new rubber washers or even add a shim of rubber or plastic. The headlight should be movable by hand without loosening the bolts, but rigid enough not to shift or wobble on its own.
