Man, AA is terrible at this. For reference, when DL downgrades you from first to coach they give you a $200 credit plus the fare difference at the time you bought the ticket. In that spirit, the previous suggestion of calling and asking for the fare difference in addition to the vouchers is probably reason. More generally, reconsider paying AA money for domestic First when they pull stuff like this on a fairly regular basis.

On the plus side, it's nice that AA at least let you know about this in advance so you can consider other options.