Oh Bert. Next you'll be telling us Santa Claus isn't real.

The relationship between sanding the connector and it being harder to unplug is purely mechanical and shouldn't be taken as a sign of electrical conductivity improving. It's true that more surface area theoretically creates a better contact, but if you think of two hard surfaces with grooves contacting one another only on the high spots, you'll see less contact surface.

I think of it like tires on a drag car: they're most effective when there's no tread and they're clean.

So, my question is, when you were testing, did you test resistance before and after? (Test at either end of the wires, not on the contact surface of the connector.) Did you try cleaning the contacts and performing the same test? How about cleaning and bending the spring contacts out a bit? They tend to lose their shape and flatten out over time.

Just throwing these concepts out there, because corrosion is not a myth, nor is the Easter Bunny.