As the owner of twenty-three sled dogs (23, no typo!) I figure I may know something about how dogs affect one's life. I wouldn't trade them for anything. I am 70 and am fitter and more upbeat than friends twenty years younger, and I have a bunch of loveable friends who can dispell any blue spells.
Bobad, Blwzabella and others have put their finger on the biggest single factor when considering having a dog: you get a dog because you love dogs and want to give them (or one of them) a good life. There are many benefits to the owner but the benefits to the dogs are equally important. I imagien the same applies to cats or any other pet.
On the : pick up every days and you'll have no problem, no smell, no flies, nothing under your shoe.
Hope this helps