I made the switch about 8 months ago, although I still do American style socially.
I think samba will be the easiest for you to transition to, and from what I've seen of the "American style" samba that AM teaches, you'll like the steps in International much better. I think Rumba will probably be the hardest to transition to as it is much slower, bent knees are used minimally, and it requires a lot more control and balance.
Paso is useful only if competing. Jive is not just faster than swing, but has some other nuances, too. I can't take jive for too long as I have some knee issues. Luckilly, it's not played socially very often :)
I think the long and short of it is that learning international will help your American style.
Having said all that, I do miss mambo and bolero, and once I'm somewhat proficient at my latin, I'm going to go back and do some more rythym.
Good luck to you. I think you'll enjoy it -- try not to get frustrated at the enormous amount of technique.