For your day in Ixtapa/Zihua you might consider heading over to Playa Las Gatas across Zihua Bay. Years ago we did a horseback trip into the beach. I know there are launches that cruise over from town to the beach. Once there you can rent snorkel gear, dine at one of the ramadas on the beach, relax in the sun, or be dragged around the bay on a large inflatable raft.

Also, virtually every one of the beach towns you mentioned will give you the opportunity to parasail along the coast.

John in San Diego