Dean's bars are gold plated, which means the thickness of gold is
extremely thin. With the current price of gold at $1300/ troy ounce,
we can't expect a pair of $5 Dean's connectors to contain very much of
it. In fact, the layer of gold on a Dean's bar is so thin that regular use will be
enough to wear out the gold, which leaves you with an exposed copper
bar that will oxidize.

Corrosion on gold connectors may be a myth, but oxidation on copper is a
scientific fact. There is no real point to sanding a copper bar,
as it will only re-oxidize. Just like any other RC component, wear &
tear will occur. If your battery connector is worn out, replace it.