I am an outsider looking in but deal with the concerns on a regular basis.
My observations are these.
1) Who are these bodies representing to? If it is government then, they will always have less impact than more science (I use the term loosely) based organisations such as the Forestry Commision. If there was weight from other scientific organisations such as Universities then these would be taken into consideration, but there is a lack of targeted research in Europe that is arboriculture specific, so forestry will always have the upper hand. 'Trade Organisations' are always seen as second tier, behind research and independent bodies. Perhaps even third tier with the advent of the online petitions.
2) There is nothing wrong with having many bodies within the same industry, all other industries have many bodies representing different aspects and views, but there lies the arboriculutral problem. All organisations trying to be everything and fighting to be the most important.
3) Europe. Most environmental bills and law comes in some shape or form from Europe these days and have done so for decades. So instead of looking inwardly, the arboricultural industry should look outwardly.There is no point in worring about things like Chartered Status and inwardly thinking ideas when the next update to European Environmental Laws will severely restrict your working practices.
4) Every day the same old things comes around, I can't get rid of my wood chip, my fuel bill is too high, what is this fungus, etc, etc. A trade organisation that represents its members would worry about these things first, and then look at the wider issues. Any house must have deep, firm, foundations.
Also there is currently too much distance between the trade organisations and education and research. It worries me that some of the best training is offered outside of the education sector (I still think some of the organisations do a good job). There is a proud tradition in this country for education in colleges and universities, just as students should be encouraged to take up training and qualifications, academics should be encouraged to get involved in arboriculture.
5) What do they offer. If an organistion only offers you tea and cake and a posh looking badge, then unless you like tea and cake, don't bother. The only badge you should need is your qualifications (however humble) and a big list of references from happy customers. The rest is down to educating the public and encouraging us all to keep learning, which is where trade organisations can help. And I mean proper training with certification, program plans etc.
6) Personally I think you are already members of the best trade organisation, ARBTALK!! There are some very important people dip into this site from time to time and with good reason. I think I am going to put ATM on my cv (Arbtalk Member) from now on.
Good on yer Steve and keep it up.