I am Portuguese myself and I think I can answer this question. First and foremost Portuguese food is not at all that hot. Spice in portuguese translates to “Especiaria” and includes everything from black pepper, cumin, red bell pepper or “colorau” to cinnamon and bay leaves. None of this spices which are the most used are “spicy” or hot (maybe black pepper) and almost none of them are used in the most famous dishes. Although our pastries use a lot of cinnamon you can hardly find any other spice in the most famous dishes from Portugal like Codfish or Cozido à Portuguesa (Portuguese Stew) or the Caldo Verde (a type of soup). You can find some stronger spices if you call them that in Bifanas that use paprika or in the famous Francesinha. You might be right when you say that the Spanish use much less spices than us though. That’s because Spanish cuisine was strongly influenced by the French in the 19th century and they do not rely as heavily on spices to season their food. As this article states:

The 19th century was one of great French influence in the Spanish cooking, due to many factors, including the Bourbon ruling dynasty who decided what was cooked in the courts kitchens. In many cases French recipe books were translated to Spanish while in France a renovation of the culinary arts called cuisine classique.

So basically gastronomic customs are interchangeable much like any other form of culture and while the Spanish were heavily influenced by the French, the Portuguese did not want anything to with them as we were invaded several times by Napoleons generals.

I could go much more in depth as this is a vast subject but I hope you find this reply satisfactory.