It is true that considering local events can really enrich a trip, especially if you're looking for cultural immersion or a specific goal like a festival. However, for most trips, especially for an average Portuguese family planning their vacation, other elements are often more determinant.
For example, for beach holidays, the budget for accommodation and weather largely outweigh the presence of a distant village festival.
The importance of events truly depends on the traveler's purpose, not on a universal rule.