KenV,
I would like to point out a couple of things:
The development of the F-18 E/F did come from the earlier F-18 airframes. But, there were changes. The length increased 4 feet, the height by a 1 foot and the wing span by 4 feet (a new wing). The maximum gross take off weight increased by 14,100 pounds and the range increased by 200 miles. This is from the US Navy Fact File. Also, from the file:
The F/A-18 E/F acquisition program was an unparalleled success. The aircraft emerged from Engineering and Manufacturing Development meeting all of its performance requirements on cost, on schedule and 400 pounds under weight. All of this was verified in Operational Verification testing, the final exam, passing with flying colors receiving the highest possible endorsement.
The first operational cruise of Super Hornet, F/A-18 E, was with VFA-115 onboard the USS Abraham Lincoln (CVN 72) on July 24, 2002, and saw initial combat action on Nov. 6, 2002, when they participated in a strike on hostile targets in the "no-fly" zone in Iraq.
This was written in 2009. There always are some problems but seemingly no serious snags on the F-18 E/F program.
As far as the engines are concerned, the F414 is a derivative engine of the F404 but with significant changes to gain an extra 4,300 pounds of thrust per engine.
One of the changes made in the F414 engines was to use one piece blisks in the LP compressor, similar to what P&W did on the F135 engines to save weight.
The F135 engine is a derivative engine from the F119 engine used on the F-22. The F135 engine is not a completely new from scratch engine. There are differences in the rear end due to afterburner configurations and total engine length due to engine placement in the airframe. The F135 engine is about 135 pounds heavier than the F119 engine due to the addition of a second stage added to the LP turbine. The F135 was designed to provide 8,000 pounds additional thrust compared to the F119 engine. So we can discuss whether or not the F119 engine was/is mature or not, but it seems to be performing pretty well with no serious snags in terms of problems.