Further to some comments regarding fuel additives causing degradation to the carb-bodies and solder-joints on (any) brass-floats.
The ten year old floats are still solid and floating. The dull oxidation appearance on the original is more from the poor soldering (at the time) then any fuel contamination. The cameras' flash makes it look worse then it actually is. The intent of polishing the floats is to possibly reduce any surface Oxidation that may take form from contact with fuel. The overall appearance benefits but is not essential to the operation.
Thanks for all the great questions and comments!