I find there generally isn't a huge amount of value to be had from using the free Amex economy-only voucher for advance bookings, but did manage to get what I consider an excellent deal from last year's making a snap decision a few days out to watch my football team play a couple of pre-season friendlies in the US - 21250 Avios and £180 tax return when cash fares were all well over £1000 return. Booking a few months out when cash fares are £400 return to the East Coast isn't really worth it IMO.