It really depends what you are looking for.
AANAC has no more information about the MDS or RAI process than is available to the general public on the CMS website--but the AANAC site does GUIDE its members to the information.
Some people learn something better in a classroom setting, some are "independent" learners. Some people find the AANAC listserv to be supportive...but just like this listserv, sometimes answers are not as "correct" as you are looking for...
Some staff who went to the AANAC certification courses felt that they learned nothing more than I had taught them over the years--the value of the courses sometimes depends on the instructor. Don't forget...to maintain certification, you must continue to pay yearly and pay for continuing courses.
If your employer feels that certification and AANAC membership makes you more qualified, and is willing to PAY for it, GO FOR IT!!
But there are ways to get information for free...HC Pro has a website which allows you to sign up for various newsletters...Caralyn Davis keeps the SNF/PPS newsletter updated...and you can get the information automatically delivered to your e-mail...and it is FREE. (am NOT advertising for HC PRO, truly...). CMS also hosts a monthly SNF ODF--free.
The MDS 3.0 will not, hopefully, have as much "mystique" as 2.0...the directions will be clearer, with less room for "expert interpretation." So you will have to weigh the value of AANAC membership...