If normal maintenance is kept up with, rust isn't an issue, then there is no reason that it shouldn't go 300,000+ miles. There might be little issues along the way, and stuff does wear out and break down with age, but the amount of money you will likely need to put into it is likely very small compared to replacing it with something newer.
If it fits what you need in a vehicle then I say keep up with it, and modify it to make it meet what you want it to do that it currently doesn't.
I starting letting things slip on mine, and I think time was just as bad if not worse than miles, and in the end added up all the little things made it not worth the time and hassle for me, I got more than moneys worth out of it, and I was emotionally attached to it, but not so much that I wasn't able to eventually let it go. It took my daughter to her first day of school and it was her first car in college. It brought my son home from the hospital, it covered 3 countries and 15 states, it protected the family in 3 fairly intense accidents, it left me once (my fault trying to push a fuel pump that gave me plenty of warning).
00 Grand Marquis LS Premium - 97 Cougar 4.6 Sport - 89 Cougar LS - 63 Falcon 302 - 82 F-150 - 97 Mark VIII LSC - 2017 Escape SE - 2012 Fusion Sport AWD