No. Digital servo's just roll a few different systems into a nice package for you.. a good deal of servo usage doesn't need to be that percise.
Yes! They are indeed worth the money if you need all of there features.. for example I am currently working on a hexapod. My hope? That it can run in the end. Yes, like an animal loping across the plain kind of deal.. but it must first learn to stand, then crawl, then walk, then move, balance, and then to run. So for now, I am buying a few 1/4 size(bigger then micro) servo's and the robot will only have 1 dof per leg. The leg joint itself. Where it meets the base and all. I will be building from there and moving into other fields(such as balance) as I need to.. but not until far into the future will I really even want digital servo's(if at all). For now, analogs are great.. and even if I end up not using them on this one, I will on another.