Thanks. In other words there seems to be little advantage for the typical American citizen to import millions of people.
Is the only advantage for the “political elite” who like to make big government even bigger?
No; since they're typically imported from countries where corruption is an accepted way of life, they won't have to fear being "found out" on bribes and such.
Also, increasing the number makes the de facto invasion more and more permanent: the official numbers for illegal immigrants is 11.7 million (of a 316.1 Million population). The real number is likely closer to 3 times as many (35.1:316.1 ≈ 11%).
Another reason to import them is because they're used to much lower wages; which means that they'll accept lower-pay for the same jobs. (And because they're illegal, they can be extorted by their employers who rely on that acceptance-of-corruption to dissuade the workers from reporting them.) — There's a few more reasons, but really money and power
boils pretty much all of them down.