When I played (I think 0.8.21) I felt very much pushed to conservation of special attacks due to SP. Don't know enough about mechanics, but just how I felt my gameplay went. It got better with the spell casters by mid to late Act 2, due to higher SP.

with the latest release you can buy SP regen necklaces in Dingirra, Jack added http://winterwolves.net/viewtopic.php?f=40&t=3423