Mmm, < .01%, it wasn't something I would've dignified with enough thought to give a number. Even as a kid, although I liked the idea of aliens, stereotypical flying saucer little green men stuff struck me as facile and absurd. A failure of the imagination as to how alien aliens would really be.

In hindsight I had not considered that their outward appearance and behavior could simply be a front, but even then my estimate would've been very low, and justifiably, I think.