There's no magic number. But with standardized specific testing like what's available, your 'odds' are certainly better. I, like many others, say better enough to be worth additional expense. How much? No magic number. Personally, I feed what I believe to be high quality feed that many others would not pay for. Though he's a personal friend, I also believe my low vet bills and very infrequent issues directly relate to breeding, feeding, exercising, etc. It all goes together. Just like with human health or other things in life. No shortcuts. None of which mean many folks won't have long happy years with a rescue animal. But there's no question your 'odds' are better with better bred, tested, dogs. 'Better' is then valued by each individual. I wouldn't by a $1000 dog. But that doesn't mean they're not worth it. It means I'm simply not paying $1000 for a pup, any pup. My choice/value determination. I don't make my living with them. I don't test competitively, breed, etc. Others do....such things make sense depending on specific scenarios. Another example: Anyone can pay very little and get chickens from a hatchery. They'll look 'right' to the untrained eye, they'll pretty well act right, and many are quite happy perpetually buying them. Then there are chickens bred to standard by knowledgeable people with an interest in such who breed for income, show birds in competition, etc. There are some that are quite expensive. I won't buy either of these because they don't make sense for me. I value health, egg quality, longevity, etc far too much to buy hatchery birds. I value my sense and wallet far too much to buy a $100 chicken. All this to say I end up somewhere in the middle and that suits ME just fine. It's what makes sense in my situation. The attributes I mentioned are definitely worth something. How much? Depends on who you are.