Even at a nominal 50 meters a day, it will take Spirit over 40 sols to get to the hills, and that's assuming there aren't stops along the way. So I don't know if it will get much farther than that. I kind of like the idea of having the rover sitting on a hilltop, just waiting for someone to come along and enshrine it.
But we'll see. NASA spacecraft have a splendid history of far exceeding their "warranties," though unfortunately the harsh Martian environment will take its toll eventually.
Everything I need to know I learned through Googling.