I don't see how you can look at the past and say it can't get any worse. Of course it can! What you mean is that AA won't be the leader in making it worse (probably Delta, as usual), and AA will just follow their lead in "enhancing value" (for shareholders, obviously).

Miles actually don't have any value. You are defining their value by taking the average price of a ticket (say from US to Asia) and dividing it by how many miles it takes. The the ticket prices change as well (they've been a lot cheaper recently, even for premium classes).
And the ticket prices change depending on how far out you book. If you want 10 cents per mile just book a one-way for a last minute on regional jet route that nobody else serves. Or a transatlantic flight to London in BA first.

If you purely want to maximize cpm, you can re-route yourself to all sorts of destinations and get it (Alaska had it at 7500 miles intra-state. If you want to fly to Adak Island that ticket alone is almost $1,000. Would you fly to Alaska just to get more value for your miles, even if you didn't want to go to the Aleutians?). But when most say "value" they mean on flights they want to take at times they want. So if there is no availability, the practical value of miles is 0. And if there is, it has gone up. So sure, the value goes up, but only because they were worthless to start (but I don't think you think they are worthless right now. Most FTers know how to use their miles, but most consumers don't).