I would reject both a trader association and a miner's association. The fact that the market is self regulating would make it difficult/impossible for an exchange without transparency and ethical operations. Having a miner's association would potentially open the network to 51% type attacks as the miners would literally be working together
Well, the exchanges now are all but transparent. Are they solvent? Are they front-running their clients? Are they faking orders and traffic? Do some clients have special privileges (like a few seconds advance knowledge of the order book)?
For a 51% attack, it suffices that the 3-4 largest miners collude. That is much easier backstage than through a professional association. On the other hand, a miner's association could better spot and sue fraudulent manufacturers, for example.
There is also a very large amount of fiat to bitcoin trade done outside of exchange and people are willing to pay large premiums to not have to deal with an exchange, much larger then the trading fees, so I would argue that the market is self regulating because the exchanges are not more transparent.
A professional association would set up a forum for miners to communicate that may not otherwise be possible. I don't think operators have a lot of interest in communicating with other pool operators, and since it would likely take more then two pool operators acting dishonestly to launch a 51% attack it would be difficult to bring at least three pool operators together like this without risking your plan leaking without this kind of foum