My understanding is Super Saver Shipping is more or less "when convenient for us". So if, like me, you live somewhere Prime trucks are on your street every day anyways, Prime doesn't offer any real speed improvement. Maybe if something is only available at a distant warehouse they won't spend anything extra getting it to you quickly but in most cases... yeah, it's still in two days.
I also find Super Saver helps me spend less: I won't order something unless my order is big enough for free shipping, and half the time by the time it is, I decide I didn't really need something or other anyways.