We've basically be doing this.

One of ours is a 2006 with just over 230k miles on it (Toyota). The last few trips to the shop for just an oil change and tire rotation has turned into large bills to fix things. I don't think if we sold it earlier we'd come out much ahead but maybe I'm wrong.

We plan to replace this with a similar 2-3 year old model and drive that one into the ground. Our other is a Ford and has not been as reliable. That will be replaced with a Toyota when it's time comes (which sadly may be with a lot less years/mileage than the Toyota).