JWST is an infrared telescope though, which doesn't really replace the Hubble. It is suited for the interesting science of our times though. An upgraded optical space telescope would probably be less groundbreaking but still very valuable to science.

> NASA really needs to just fill their telescopes with gyros upon gyros

It’s an interesting tradeoff. Missions are designed (and costed) for a nominal mission lifetime; adding more redundancy increases costs. But it’s true that the successful missions tend to stay in operations much longer than their normal lifetime.

If feasible, sure.

But I'd expect it's often cheaper to send up a new telescope than to repair an old one.

That’s a bad faith take. The OP is clearly expressing their opinion that space exploration is underfunded. No one is unhappy the Hubble is going on 35 years. Think how much we would be learning if we had additional similarly scoped astronomical missions in 2000, 2010, and 2020 though.

What was cutting edge in 1990 is very far from it today.

Sending up Hubble II and Hubble III would of course not mean that Hubble I stops being used.