Do the work in small steps, getting the most critical parts that are about to fail first.
I have a 1996 Explorer, cannot tell how many miles, the odometer stopped turning at 154000 miles 6+ years ago. It does not use oil, has never let me down. I replaced the ball joints and shocks on it and put on a new a/c compressor. It still rides and drives as well as it ever did, and I would not hesitate to keep fixing it until I hear some death rattles from the engine.
I chose to put a little into repairs on this one since I know what I have, I could have stopped and bought something a little bit newer, but then with an unknown used vehicle who knows what problems will crop up.
I too subscribe to the use it completely up before replacing. All of the repairs on this Explorer over the last 6 years of ownership equal less than 1 year of car payments, not to mention the savings on insurance and taxes.
If you like the car and know that is all that it needs fix it.