Indeed, have nice breakfast, lunch or dinner in a restaurant located on the beach is nice but always is the expensive option. But when you live in a place with no beach or with a cold weather it seems a great option the restaurant on the beach.
My recomendation is always see how full or empty is the restaurant, you can ask to come to see first if you see a lot of people enjoy the meal is a good since. other options is to see the menu, a lot of restaurant in Puerto Vallarta Malecon or los muertos beach has a hostes invite you to come, watch the menu and see the prices.
A nice restaurant always have great fornitures and great location, and many time this is what are you paying for. The view, the sand in your feets, the sun in your skin reading your favorite book or just drinking a nice beer or wine.
The prices in a good restaurant on the beach are expensive but whort it, my recomendation on the los muertos beach in Puerto Vallarta is El dorado, La palapa and Daiquiri Dicks. In Nuevo Vallarta is dificult to find a restaurant on the beach except for those inside the resorts. But in the Bucerias area my recomendation is the fat boy located in the downtown of bucerias.
Of course this are only my personal recomendation and dont mean the others restaurants are not good. But if you gonna pay $10 USD per dish or maybe more, make sure the restaurant is great.
Thanks for your support, sorry for my writing and grammar i still learning english. Saludos amigos :)