One (behold) is certainly rarer and more formal than the other.
Nowadays I believe is is only found in the phrase "lo and behold" wich is generally used humourously to express surprise : ( qui voilà ?/ qui vois-je ?)
we were sitting at a sidewalk café and lo and behold, my sister walked by
I agree about the poetic side of "behold", but there are also connotations of "wonder", and "amazement" when you behold something. Beholding something would be more "mind-shattering" that just "seeing" it. And if I am not too bold, I think "behold" is for a crowd, rather than an individual. It is for "all", rather than "one". I have not even looked up the definition in a dictionary - I just give you the "gut" reaction to the word, since I first saw it used many years ago. Behold would also be used in the written form, and probably not in the spoken form. The bible is the place where it is most used.
I think behold is rather taking in the whole of what you are looking at (as Texasweed said, "more intense") and see is simply that you see it, nothing to it, just the physical fact of your eye focussing on a certain object.