I think this is more a question about personality than it is about the hardware.
Will the hardware last 20 years? Good chance it will, especially if you take care of it and get regular maintenance.
Will you want a new machine before then? Only you can answer that! For me, the answer is, "Probably yes". Will I actually BUY a new machine before then? I can't answer that yet, I don't know what kind of awesome upgrades they will come out with in the next two decades! (But probably YES again!)