It's just "Let's see what happens" - and that's why it's a bad idea.

LHC was justified as a search for the Higgs. The Higgs was found. Everyone was happy. Fine.

LHC 2.0++ is just banging rocks together for the sake of it. Something interest might fall out, or it might not.

But considering that we still don't understand quantum origins, have no clue how to make a theory of quantum gravity, and have no idea what Dark Energy is, or even if it exists at all, it might be better to spend the money on pursuing creative theoretical leads in those other directions and coming back to country-sized experimental hardware when there are some new theories to test.