Assu sutta and similar suttas like Mata sutta etc., which have been quoted many times before, clearly state literal rebirth. I think, the Buddha cannot be more clear than this about literal rebirth:
"Excellent, monks. Excellent. It is excellent that you thus understand the Dhamma taught by me.
"This is the greater: the tears you have shed while transmigrating & wandering this long, long time — crying & weeping from being joined with what is displeasing, being separated from what is pleasing — not the water in the four great oceans.
"Long have you (repeatedly) experienced the death of a mother. The tears you have shed over the death of a mother while transmigrating & wandering this long, long time — crying & weeping from being joined with what is displeasing, being separated from what is pleasing — are greater than the water in the four great oceans.
Now, the important question is whether understanding of rebirth is useful or not. I think it is very useful (although not essential) and related to the goal, otherwise the Buddha would not have put so much stress on it. It is connected to dispassion and release:
"Why is that? From an inconstruable beginning comes transmigration. A beginning point is not evident, though beings hindered by ignorance and fettered by craving are transmigrating & wandering on. Long have you thus experienced stress, experienced pain, experienced loss, swelling the cemeteries — enough to become disenchanted with all fabricated things, enough to become dispassionate, enough to be released."
And his words right after awakening:
Through the round of many births [Anekajāti] I roamed
seeking the house-builder.
Painful is birth
again & again.
House-builder, you're seen!
You will not build a house again.
All your rafters broken,
the ridge pole dismantled,
immersed in dismantling, the mind
has attained to the end of craving.
http://www.accesstoinsight.org/tipitaka ... ml#dhp-153
The important thing is to understand such literal rebirth within the context of the Buddha's teachings about anatta, and that what we call literal rebirth is actually rebirth of relative experiences in one of the different relative planes-of-experiences as conditioned by past mental development.