We've got the cats insured, and for us it's been worth every penny - both Bear and Robot have been very ill, and run up very expensive vet bills, and in both cases it was very good to be able to make decisions about treatment without worrying about how to pay for it. Robot, in particular, cost thousands of pounds, because she ended up staying in a specialist cat hospital for three weeks with associated surgery and all manner of other treatment. She's such a cheerful and placid cat that she thought it was a great adventure and was very unbothered by it all, and it bought her several years more of happy cat life. She was diagnosed with cancer about a year ago, and we decided not to treat it agressivley because it wasn't going to be cureable - just postponeable. Even there knowing that we had insurance was good - we could be sure that we were making the decision based on what would be best for her, and not for our bank balance. She's baffling everyone with her liveliness now - she's a bundle of skin and bone and tumor, and still cheerful and purring and bossing the other cats about.
Sorry, I'm rambling. But yes, I think, we've found it very useful but we have claimed for more than we've paid for it, by a long way, because Battersea gave us such defective moggies. Neither of the cats was particularly old when they got ill, and in both cases there was enough of a chance that they'd be sorted out, and healthy again afterwards, that I had no huge qualms about it being unfair to them - although that was something I thought about.