I had to face exactly this on an old commute. Dipping the front light was absolutely necessary in a park and another stretch of unlit bike path. It was a bright enough light to illuminate the road, though not well enough to ride at any decent rate on low power.
The solution I found to this was to add a narrow-beam head torch. This can be dipped hands free, and points where you look rather than where the bars are pointing (quite useful when it's pitch dark and you're next to a lake going round sharp bends). Overhanging branches can mean the need to illuminate stuff that's not the road surface, so I tended to adjust the light as I rode much as you'd switch from main beams to dipped beams in a car.
The head torch I bought was ~5 from dealextreme, and is 150 lumens nominal -- so not very much ligfht in total. But all that light is in a bike-sized area of road even if it's directed 10 bike lengths away. I tended to adjust the angle such that I had to tip my head slightly up to illuminate as far away as I'd like for ~30km/h speeds on imperfect tarmac, so that a natural head position was more suited to slower speeds with other people around. In busy areas well-lit I could easily point it almost straight down.