Look at meals on board--dinner tends to be more worthwhile, including wine. (Alcohol might not be served at all times of day, depending on the carrier and route.) Does flying in FC save the cost of a restaurant dinner in an expensive city?

Also look at how many miles coach would cost versus FC. For example, most domestic RTs on DL cost 40,000 miles for medium coach but 45,000 for low FC. The extra 5,000 miles for guaranteed FC (no waiting/hoping for the upgrade) and a better choice of seats can seem very much worth it!