I dont have insurance on any of my cats because there are that many, that it costs less in the long run just to pay the vets bills. What I try to do, and it takes a lot of self-discipline is keep a cat fund in a separate account, so that whenever I sell a kitten it goes back into that fund, and goes on to any further vets bills. I have had to add my own funds to it btw which just shows that there is no profit in cat breeding
On the other hand if you only have say up to three cats in your household, I would recommend getting them all insured, or indeed any pet only household. It would be worth your while in the long run. Breeding catteries and multipet households are what make the vets the millionaires that they are, lol.