This is a first for me... Just got a call, apparently AA just changed my flight to an all coach flight and said I'd get a $75 credit/passenger... The 1st class cost more than $75/passenger (compared to the coach price) at the time I booked --- do I have any recourse?

So this was an express flight? Was it a CR7/9 down to an ER4? What cities to and fro?

You might have been offered courtesy vouchers versus the fare difference ($75 is a very exact number) so it merits a call to request the fare difference in addition to those vouchers. If you want to keep your seats in F and there is an earlier/later flight in the day that offers it (with seats open in the same cabin) you should be able to have it moved on a one-time basis at no charge. Good luck and post back with your results!

It would be helpful to know what the segment is and if the AA call was offering an actual fare difference refund or AA vouchers.

Are there other flights on AA with first class that will work for you? If so you should be able to ask to switch to those flights.

Otherwise, you could always ask for a refund and rebook (either to another airline or to AA in coach if the price is still cheaper).

I'm thinking that the possibilities for recourse are numerous. You could probably get your choice of:

• A full refund with no penalty
• A credit (back to your credit card) of the difference between what you paid for FC on that day, versus what coach would have cost that day
• A change (with no fee) to another flight which offers FC on that same day of travel
• A change (with no fee) to a flight from a nearby airport which offers FC on that same day of travel
• A change (with no fee) to a different day of travel
• etc.

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.

Do you have documentation of the difference in cost between coach and first class at the time you booked? Many of us recommend taking screen shots of the fare grid whenever purchasing first class, for this reason.
Also, is this just one leg of a multi-leg journey to your destination, or is this a simple one-way/round-trip?

If you don't have documentation, you can try providing us your specific flight details, the date of original purchase, and the fare you paid, and someone can use a service like ExpertFlyer to determine what the fare difference might have been.

After you have the documentation, your steps are to (1) contact AA, tell them the $75 is insulting, and request the fare difference returned to original form of payment, plus some type of "customer service gesture" because of their insulting offer, perhaps 5k miles or a $50 voucher; (2) File a complaint with the Department of Transportation; and then if all else fails, you could (3) sue AA in small claims court, which is relatively easy to do and would likely result in a settlement.

DOT rules certainly allow for schedule changes and aircraft substitutions. If AA provides a refund as described in the contract of carriage the DOT has no interest.

(emphasis added).
Who cares whether or not the DOT is interested, you can still file a complaint.

Besides, the CoC is notably vague, only calling for an "appropriate" refund in the Oversales section. The argument is whether $75 is appropriate, and there really should be no argument if the actual cost of FC was more than $75 greater than coach.