I used to have VPI for our first greyhound. I did find that, for him, it was a good plan because he had a habit of hurting himself or getting sick in a major way about every 18 months, and every time the plan paid out so that I remained ahead of the game. But!! It would have been a losing proposition for the other three hounds we've had, since they've been more low-maintenance. If you think you have a pet that's likely to get some sort of cancer I think insurance is a good bet, but otherwise you may do better to just put the same amount of money that you'd pay in premiums into a special savings account - you'll likely find that that amount you have in savings will cover whatever expense your pet racks up at the vet.
And . . . (stepping up onto my soapbox) . . . the best insurance you can have if you have a dog is to brush their teeth every day. It's so very much cheaper to keep their teeth clean than it is to pay for veterinary dental cleanings, and dental disease is such a preventable illness, yet it can have a severe impact on your pet's overall health.
. . . stepping down now.