I too have a RWDS Amex and it only makes sense (fee wise) if you would be using the extra card. Since I am it makes sense for me to have it. Then it spins off nice bonuses like: "1,5XX base charging and 1,0XX Rewards Plus Bonus" in one month. Mine is getting less use now that I have a Starwood Optima. There you get a 25% bonus on large transfers to airlines and AA and UA are included. The bonuses are nice especially if you are flying/staying on/at partners and don't want to have a card for each partner.
Perish the thought but the bonuses are nice even when you charge a WN ticket.
BSL