I looked into pet insurance when I got my pets several years ago and after reading the exclusions and doing the math, I decided to set aside an emergency fund that I could use for vet expenses instead rather than paying a monthly premium. Like any insurance, it’s a hedge against expenses you may not incur, so just speaking for myself personally, I was willing to take my chances that I could cover any necessary expenses out of my savings. So far the pets have been fairly healthy and it’s worked out in my favor, but I expect that the vet costs will go up with time.
Especially if you are insuring an older dog, make sure to read all the fine print. I think PetPlan is one of the better ones in terms of fewer exclusions, covering actual vet costs rather than “customary” costs, and the like. I have heard bad things about VPI (low/no payouts, looking for any excuse to deem something a “preexisting condition,” etc).