USA dollar bills (though not the coins) are widely accepted in most tourist-oriented restaurants and shops around Puerto Vallarta. Do pay in Mexican pesos whenever it is possible, however, if you want to get a better price and not lose money.
So in the end, you don’t need to bring large amounts of dollars, in the past, when banks were primitive and ATMs didn’t exist, maybe, but not now. Pesos are king and you’ll normally just get a bad exchange rate and lose money.
Even so, I would recommend bringing a few hundred in cash as plan C 🙂