Dominion Seaside Treasure Map: do both copies activate?
You play the first, performing its action of trashing itself and the second Treasure Map and gain 4 golds. You can't continue to play the second Treasure Map since it's no longer in your hand.

You also can't use Throne Room to gain more than 4 golds since the text states "If you do trash", and you can only trash a card once (I also tested on isotropic to make sure)