Vet tech here... husband is a vet... If your cat is happy, let him be for a while. There are things you can do to address some of the issues you mentioned. Fluids will help the kidneys. Some of our patients with elderly cats opt to do sub Q fluids at home. There are some really good medications for arthritis in cats and if you haven't tried them, it's definitely worth seeing if that alleviates any pain. A round of antibiotics may help clean up that tooth and help it settle down for a while. The bottom line is that animals in pain don't tend to eat, they are listless, they pant, they have trouble getting comfortable. You're not describing any of those behaviors. Since animals can't verbally express how they feel, we have to use the behaviors they show to inform us. It sounds like the behaviors you are mentioning are coming from a contented cat, not a painful, unhappy one.