For me, like Pinniped, being based out of MCI, my personal choices (mainly) are currently AA, YX, UA, & CO. I don't/won't fly DL. Since we're not a hub for anyone, we're looking at a stop to most places (with some exceptions) and my clients are not extremely price-sensitive. That allows me to fly AA on some of their higher fares, primarily to the West Coast.
If MRTC went away, I could hopefully bank on the new upgrade program for EXP's. But since my schedule changes daily, I would be out of luck since I can only book about 48 hrs ahead of my flight.
Since I do about 150K miles/year, (AA currently gets about 125k out of that), it would probably drop to around 25-50/yr.
My other choices... UA has mostly the United Shuttle flights to DEN (no E+) and regular flights to ORD. CO is all RJ to EWR, CLE and IAH (one 737/day, all others are Embraer's). Southwest is Southwest (Midway, shudder) and YX has the cookies (man, those are good). I would switch most of my business to YX where possible and then to UA.
In short, since I'm 6'4", MRTC means quite a bit to me (sorry for the pun).

Safe travels.