You can never go wrong with too many grounds. I work on a lot of British bikes and cars,,, Lucas Electrics are known as the "Prince of Darkness" 3 positions of a Lucas lighting switch are "Off, Dim, and Flicker"
So, i add grounds for all components, Next to each part (Headlight, taillight, indicators, reg/rect., Electronic ign brain box, etc etc) I run dual grounds,,one right to the frame or brackets its attch too and a second wire running to a central ground, usually at the main frame structure near the battery location.
So, it seems to me, especially with such a voltage and current sensitive bike as these Buells are,,,, that extra grounds and updated grounds are very important. Also, dont take your connections for granted. Motorcycles are all "Built to a price point" in other words,, compromises are made. Consider better grades of wire, and terminals, learn to use a multi meter. and add a voltage gauge to your bike. I would bet the above problem would have some indications with fluctuating voltage readings. Clearly the connections were heat sensitive.