IANAL, but I suspect if you could document your spousal relationship with a marriage license or other civil union documentation, AC would likely grant you the spousal discount. Even with such docs, depending on the leanings of whomever was processing the membership or their management, you may still need to fight it. I don't claim to know AA's corporate or social policies here.

But, if this is something you are genuinely after, I think there are better ways to approach it than an oh-by-the-way addendum to a letter complaining about the product and price.

Not intended to be a political message here...