I've been standards accredited for awhile now and recently retested for renewal. You do need to be prepared for the test and be alert while you take it, but its not too difficult to pass. Hard to say if its worthwhile as it seems to me that very few people in the boating public are aware or interested in ABYC, which is unfortunate.
I do value the standards and quote them in my surveys, but as has been pointed out, the website is a mess and there is a general sense of disorganization. The standards are written far better than the CFR's but its my opinion ABYC does a poor job of public outreach and does not always provide a great value for the members. With that said, in a fairly unregulated and sometimes unscrupulous industry, its one way of separating yourself from all the self appointed experts.