Who cares if the original mission lifetime was conservative.
If it's like a toyota and everything is going wear out at once, so there's no point in replacing the alternator because the engine and transmission are weeks away from failure too, then I agree with you.
But if it's like a 59 Chevy and the tires are old but the engines still purring, then don't dump it. Give it to the kids and let them play with it. It's not like it's learned everything it can learn, and we need a new bigger scope to make advances. I'm not saying don't build a bigger scope, but the cost of maintaining and continuing to use this one has got to be relatively small at this stage.
It is $1.5 billion baseline for each repair mission. Using the car analogy, at some point the monthly repair is more than payments on a new one.