FWIW, here is my opinion:
I only belong to my local Arborist Association and have now for a few years.
When I first got certified by the isa, I joined all of the groups except for ASCA.
Over the years, I became disappointed with the reality of 'joining' these organizations.
About the only real benefit for me was the magazines and they are all to often a platform for adverts.
Every once in a while I would check out some article that was good, but overall it was like reading a commercial.
ASCA: They charge (last I checked) about 400 bucks a year.
As a isa certified arborist, and a working kind of guy, I have yet to see how asca can help me make more money UNLESS I go full time with report writing.
TCIA: Part of the membership requirements are that you state your income. Your income determines your rate for membership.
Sorry, but that is very very personal. Based on how I present myself to the IRS, and how I manage my own personal finances, I just cannot believe that any one ( or company) gives a truly honest answer to that requirement.
So I, personally, feel that this requirement is inherently dishonest.
So I don't participate.
I have narrowed down my professional affiliations to belonging to my local arborist association which promotes the WORKING ARBORIST IN THE FIELD.
That is important to me, not the corporate stuff. I would like to know the tricks and methods which teach me how how to improve the working conditions and plant health care knowledge of the person who actually has to do the work (me!).
Sorry for the long reply but I feel strongly about what all this 'membership stuff' means for the person who is just trying to pay the bills, do a good job, and maybe, just maybe, be able to call themselves a tree care professional.
Here is a link to the org. I pay dues to:
http://www.cal-arb-association.com/