If your 6v system is “clean” and working well, and you do not need/want 12v devices, why not stay with the 6v?
Bad grounds and small battery/ground cables are the reasons for unreliable/weak 6v systems. These are easy to remedy and/or easy to repair/replace.
My 6v generators/starters/bulbs ignition-parts cost as much to replace/rebuild as do my 12v parts.
