Are they important to getting business?  I think the answer is no...and yes.  I don't think that the majority of the consumers care what letters come after your name because most won't have a clue what they mean anyway.  They're not as well known as such things as PhD, MD and DDS for example.  A few may choose someone with a designation because it LOOKS impressive, but it's still the service afterwards that will make the difference.

That said, I think that choosing the right designations to get may help you get more business because it's the LEARNING that happens in getting those designations that will improve your business performance (or at least, give you the tools to do so).

Which ones are best would depend on what your focus is going to be.  For example, going after a buyer's specialist wouldn't be much of a help if you're primary focus is going to be on listing property.