Don't rely on efficient grounding via metal parts, it is vulnerable to corrosion.
I don't understand this statement. Every connection on your motorcycle aside from the soldered one are mechanical interface connections and even solder could be considered a mechanical interface.
You must mean unprotected connections such as bare steel. In which case use grease or paint to protect the connection.
Also, don't get confused by the term "single point ground". You might imagine 20 wires connected to the positive side of your battery
. Usually there is only one or two wires going to the battery
ground, then a point on the frame where the grounds are distributed. And I disagree with the idea that the frame is not a good bus bar for ground distribution. This is common practice in electronics. Unprotected bolted connections or expecting the head stock bearings to be proper grounds is the usual mistake that folks make. The next are broken bullet female connectors. Those can be a bugger to find.
I make liberal use of dielectric grease to protect electro-mechanical connections. Especially helpful in handlebar switches which have a brutal life.
Poorly grounded condensers will make your life miserable as I recently found out with my old 6T. The internal ground in my distributor had managed to gain some resistance causing hard starting and occasional miss. I corrected this by tightening the two screws that hold the Bakelite points platform to the distributor body and restoring the mechanical interface ground connection.