The problem is you don't know how much time you gain or do not gain any...a few years to a dog is a long time or you can defy odds & gain alot, rare but happens. It is hard personal choice...to each thier own. I'd give it a shot for 3 yr old dog. You can always euthanize if things go wrong, but once you euthanize, no more choices,just a ton of $. It is such personal thing..no right or wrong. You do what you can live with.