Just to give an example, of the 4 major parties in Mexico, 2 are members of the Socialist International, 1 is Maoist and the 4th, considered their center-right party is about where the Democrats are economically.
As far as the vast majority world (well that which isn't Muslim) is concerned, our most milquetoast Republican is a radical right winger. Why would we want the electorate of these countries moving here? On the off chance you might get a Cuban or a Vietnamese or two to vote for a tax cutting politician?
Not even close to worth it in my cost/benefit analysis.