Funny enough it actually mentions in the Wikipedia article that most Americans are unfamiliar with the slur. I'll be honest without this thread if I heard someone say it, I would probably have used it unknowingly just assuming it was similar to Aussie or something.

This is not to make light of the slur, but if someone called me an "Ameri" I would probably just assume they're French, which might be meaner than anything they're trying to say to me.

Is Spaniard not the correct term?

I’ve heard people say “Pakis” as a short for Pakistani in a non-insulting way

Non-insulting according to whom? Some people are so ingrained to racism that they don't even sound racist. It's like old people who say "negro" but don't mean to offend. They're just unconsciously recycling the racism in which they were indoctrinated.

Ah, but it is such a fun word! Shortening it takes out the fun of saying the full Pakistani.