I seriuously doubt there is much of anything you will want to see in La Paz. I recommend you try a ship tour if they have one like snorkeling.
If you are in luck there may be some wildlife in season. The Sea of Cortes has a LOT of amazing wildlife; porpoises, whales, sea lions, etc.
If they say they have that - do it. save your shopping for Cabo - it has the best shopping on the Mexican Riviera.