"But replacing the fork, brakes, shifters, crank, casette, deraillers & wheels/tires seems be an expensive endeavor."

It is, I've been down this route before. The Jack would be perfect for me but I'm not a strong cyclist and need the extra gears. So it's the Espresso, and maybe just a stem swap if the bars or too high, or a new folk if I do more muddy stuff. I don't know if bike disk brakes wear unduly, maybe the pads do, but chains and cogs wear, and that's usually been my biggest expense.
Having said that, my 15 year old MTB is at my pal's house, the only thing he's replaced has been the saddle.. I bought it in 1993 and nothing has worn out yet....