Whether you keep what you have or buy a new car, you’ll still have to do maintenance.
Whether maintenance is a fixed cost or a variable costs depends on how much you drive your car. Maintenance intervals are usually based on mileage/time intervals, whichever come first, so if you don’t do a lot if driving, maintenance becomes a fixed cost. If you drive a lot of miles, maintenance becomes a variable cost.
Having said that, when you compare a new car to the car you have, I treat maintenance as a fixed cost for the purpose of comparison, because maintenance should be performed on any vehicle, whether it is new or old.
What you should be considering are repair costs, and it doesn’t sound like you have any to speak of. I know what that is like, because I drive an old well-maintained Honda too, and the repair costs on my 16-year-old Civic with 257,000 miles have been minuscule.
Buying a new car won’t prevent you from “pouring money into maintenance.” It will, however, lessen your odds of “pouring money into” repairs.
So the real question is, “Does this old car require frequent repairs?” If the answer is “no,” I think you should keep it. When stuff starts breaking, and repairs become frequently necessary, it will be time to buy another car.
Even when repairs become frequently necessary on a car, keeping what you have is almost always less expensive than buying a new car, but nobody wants to deal with frequent break-downs and lost productivity while the car is in the shop, so at that point the decision usually becomes a pragmatic decision, not a financial one.