CC - It's not the billions spent developing the C so far. It's the remaining billions on completing and testing the mission systems so that they do some of what the Super Hornet already does, and the billions more that's represented by the difference between the price of 260 Supers and the price of 260 F-35Cs...
Not to mention the comforting feeling of being able to fly 500-600 miles from the carrier with one engine... In a jet that weighs 5,000 pounds more than a Super, with the same thrust... When the Super community is pretty comfortable taking on all comers with the help of Growlers and Harm/AARGM...