Does your calculus change when the older vehicle has low mileage?
I ask because I have a 7-year-old car with 43K miles that I like very much; but, eventually, I expect to encounter age, rather than mileage, related issues. (I am already concerned about tires, age not wear, which will not be cheap for this particular vehicle.)
Sounds like a keeper, at least for a few more years, given that you like the car and don't report major mechanical drama. Perhaps you'll get another 3-5 years out of a set of new tires and brakes, when needed. These days, 7 years and 43K miles doesn't seem much.
Unless you really want new car, I'd be inclined to bite the bullet on the new tires, and drive for at least few more years. I wouldn't worry too much about what will eventually happen as the car succumbs to plain old age, regardless of mileage. Expensive non-wear items (not tires, brakes, fluids) will start to fail more quickly and you'll get tired messing around and poor reliability.