a well-spent and carefully thought-out mouse

Here's my take, Stacy.

Her amusement was usually a bored response similar to that of a cat that normally enjoys an active and wild chase of a mouse. It would get little to no reaction from said cat watching a very tired mouse that had engaged in much exercise.

What does "well-spent" and "thought-out" mean here?

I venture 'well-spent' means exceedingly tired. Possibly 'thought out' means that the cat has considered that the chase of a very tired mouse wouldn't be at all exciting.