As JTO says, even the early F-16A/Bs were able to be upgraded into very effective aircraft, using newer technology than the initial F-16C/Ds.
Hype about "they can't get rid of them fast enough" is an inaccurate way to describe the UK Typhoon history. The fact is that the 1998 production contracts were only marginally smaller than the Cold War figures originally envisaged, and don't reflect today's force numbers, while the contractual structure makes it very difficult to cancel later aircraft, and easier to retire older ones.
The future of the F-35 is likely to be more like that of the F-22, with slow, expensive and marginal upgrades aside from catching up with the state of the art in weapons technology.