Without being in either breed so having no experience, I'd say the main difference would be that the Portuguese is a Working breed and the Spanish is a gundog -you tend to find quite a difference in behaviour when you compare two different breed groups. With the exception of Utility which really is a mix of a lot of breeds that didn't fit anywhere else, and the Toys that are classified mainly according to size, you do (generally speaking) tend to find a somewhat similar temperament between dogs in the same breed group.
Although what Marianne says regarding breed groups being similar, Spanish Water dogs are different from most other gundogs in that they do guard and also herd and it helps to remember this when training and living with them. They are fabulous dogs, intelligent and quick to learn and to work things out for themselves, especially if you don't work their brains. Needless to say they're more likely to think of the wrong things themselves rather than the right!
I've always assumed that both these breeds would be similar temperament - I'd have thought they have a lot of common ancestry given where they come from, their appearance and the job they do.