Well, I have never studied italian nor portugeese. I struggle to understand about 50% of a subject I know in a very formal italian, like the news. If I don't know the subject it's over. I have italian friends and coloquial spoken italian is impossible, even if they don't use any special jargon. Portugueese (brazilian at least) is a complete different deal. I have never learned a single word of portugueese and have always been able to 1) understand someone who speaks with a so called "standard" accent and 2) be understood if I use a "standard" accent in spanish.

I'm a bit worried you're asking that if you know Spanish, you'll therefore understand (and be understood in) Italian. You'll see the parallels, but I think it's better to treat them as independent languages.