Well you have to go into caves to get materials to get the machines at least once. And I still do. I and many other players only "automatically mine" in terms of quarries and tunneling, and not cave exploring.
Either way though, I still hate having to go into caves. Depending on how deep down you go, it's incredibly dangerous and unnecessarily creepy, what with all of the various "cave sounds" that happen to play.
I find more fun in seeing how far I can go in terms of automation and efficiency. Sitting around and waiting for diamond generators to make your resources is obviously going to be boring as stuff; the fun is making your diamond generators faster, more energy-efficient and perhaps make more than just diamonds.
An interesting system I'd like to implement is pumping in lava from the nether into the overworld through the means of ender chests and dimensional anchors to power magmatic engines.