^Interesting thought, but ENT kind of established that Earth hadn't had much contact with other aliens besides Vulcans until NX-01 was launched. They hadn't yet met the Andorians or Tellarites, just a few species like Vulcans, Denobulans, and Draylaxians.
Then maybe the saucer influence comes from the Denobulans?
I don't really buy it - our own cultures, even without Trek, already have plenty of images of saucer shaped spacecraft, so certainly someone would have played with the idea without (additional?
) alien influence. Then again, maybe one of the founding races of the Federation that we haven't seen ARE the "little green men" that abduct people to put stuff in their butts and turn cows inside out, so that influence is from them, after all.