Take what action?
Using a free speech defense is not going to force the US government to do anything in particular in response. It will not force a definition of currency, nor would such a definition by the supreme court cause the result you are contemplating (AML law authority reduction), it would instead do the opposite and cement the AML requirement, like MoneyGram.
In any case the issue would have to rise to the supreme court of the US before it would have any meaningful constitutional impact, which is not likely.
Despite this:
http://bitcoinmagazine.com/5027/freedom-of-speech-in-financial-commerce/
Commercial speech has LOWER protection with respect to freedom than other speech in the US.
http://www.law.cornell.edu/wex/commercial_speech
Ohralik v. Ohio State Bar Ass'n, 1978:
"To require a parity of constitutional protection for commercial and noncommercial speech alike could invite dilution, simply by a leveling process, of the force of the Amendment's guarantee with respect to the latter kind of speech. Rather than subject the First Amendment to such a devitalization, we instead have afforded commercial speech a limited measure of protection, commensurate with its subordinate position in the scale of First Amendment values, while allowing modes of regulation that might be impermissible in the realm of noncommercial expression."