Hello again, grizz;
should you decide not to do the beach thing at El Cid, you should still see the Golden Zone. It's the best place for shopping and you should at least see the beach. Just have one of the open-air taxis drop you off and roam--you can't get lost. The Aztec Theater is there where you can see a flolkloric show and the famed Papantla Flyers, a great aerial act. Lots of good sidewalk cafes, cold cerveza, and the hotels are right there should you change your mind and want to take a dip.
Not knowing your interests it's difficult to say what a "don't miss" would be for you. There are trips to villages in the foothills of the Sierra Madre; golf; the sportfishing is great in Mazatlan. If you really want to get a feel for the place and the people, we've done the walking tour of the old downtown area with the Cathedral and the markets. You can hike or take a cab to the lighthouse on top of the hill near the harbor entrance for a spectacular view of the whole city and coastline. And of course the Pacifico Brewery Tour is always fun--especially at the end when you get to try the product.
If you are doing the classic 7 day (Puerto Vallarta, Mazatlan, Cabo San Lucas), my suggestion would be, sightseeing in P.V., shopping in Mazatlan, and water activities in Cabo. P.V. is the most scenic; Mazatlan has the best prices; Cabo has the best beaches. (Please don't flame me if your favorite beach or botique is in P.V.--I'm speaking in broad generalities here)
So there you go grizz; one guys opinion.