As a relatively fluent Spanish speaker who can't really understand Portuguese and finds Italian completely unintelligible, I think you're using 'mutually intelligible' pretty loosely here.
Spanish speakers are a huge group and many simply don't know their own language. It's like going to Alabama and expecting to find Shakespeare.
I'll grant you that mutual intelligibility is difficult to define but I'm using it in the sense that my wife is conversational with folks from Portugal and Italy when we travel there. That's a decent standard.
But then I am a poor benighted bastard living in Alabama.
Of course, I lived in Texas until about 8 years ago, when I moved to AL.