Agreed. The engine, keel bolts, and standing rigging/mast should be bonded together for corrosion protection and to provide a path to ground in case of a lightning strike. They should never be used intentionally to carry current.
The electrical system on these boats is aging. I had an overhaul done a few years back. Brand new power and negative from the battery switch to the panel. Also, the panel itself isn't that well built. There is no hot bus bar; rather, a whole mess of crimped on terminals on short jumpers daisy chains one circuit to the next. The result: A lot of resistance and voltage drop! Since I wanted to keep the original panel, I had a hot bus installed, which connects to the battery switch through the main fuse (located near the battery.) Then an individual hot wire runs from the bus to each panel switch. The voltage drop at the panel pretty much went away.
Shore power presents its own concerns and dangers. I suggest getting a good book on marine electronics.
