What is the max mileage on an old Infiniti?

I have a 1994 Infiniti q45 with 175,000 miles and a bad injector. I'm wondering if its worth paying $800 plus to get it fixed, if its going to die on me soon anyway. I take pretty good care of the car but I commute 80 miles two days a week and I'm not sure how much more mileage it can handle or how much longer it will last me. Any advice?