I am a great believer in good earths and earthing. When you route the earth via the frame, there can be all sorts of paint, loctite, anti-seize, grease that gets in the way of metal to metal contacts and builds up resistance. As well as the main frame earth, I always take an earth up to the instrument cluster so I have a guaranteed good earth up there. I sometimes do it at the rear too. Tracking down earth problems can be the devils own job, so I prefer to over-engineer by a couple of wires or so.