Hola Jim , My husband and I live full time in Vallarta! That is cool you are coming.
So far I have not found any McDougallers here, other than 1 woman who is here part time. There is a Vegan FB forum for PV. Quite a few vegetarian restaurants with Vegan options but sadly most use oil. Vegetarian Planet is a buffet style restaurant near the old cathedral in Old Town but again so much oil. We do best just cooking our own.Or buying fresh things and picnic. Great fresh fruit and vegetable market downtown and a Saturday market during high season.
Barra Light is an option in downtown ,not far from the pier, and they have a branch in the Marina Vallarta where I am. They have a salad bar and sandwiches. There are small pocket vegetarian restaurants in Colonia 5 de diciembre. Hard to get the no oil tho'. Lots of fat free corn tortillas available here that is a plus. This is really low season and quite a few places are closed for the next couple of weeks. On the other hand Hotel prices are at their cheapest!
Where will you be staying? And when? You can pm me. Dlee
Would love to meet you and your wife.