Does Hermès hardware affect resale value?

Yes.

Gold hardware and palladium hardware can both be highly desirable, but the combination of bag color + leather + hardware matters more than looking at hardware by itself.

For example, a particular color paired with gold hardware may be significantly more desirable than the same bag with palladium hardware or vice versa.

This is why professional valuation should examine the complete configuration.

Should I keep my Hermès receipt?

Yes. If you may eventually sell your bag, keep everything.