Are 24k plated gold coins worth anything?

No, they are worth no more than the metal (or face) value of the coin, the gold plating adds so little gold that it would cost more to de-plate the coin than the gold is worth.

For example, a 1965 gold plated half dollar would be worth ~$4.50 in silver scrap just like a normal 1965 half dollar. A 2002 gold plated quarter would be worth just a quarter, just like a normal 2002 quarter.