For serendipity to work its magic you need to be able to explore the solution space. In high energy physics that usually means putting more energy into a system

For serendipity to work its magic you need to be able to explore the solution space. In high energy physics that usually means putting more energy into a system, as (naively said) that will increase the amount of stuff that will happen. So I'm all for building bigger and bigger accelerators, even if they cost trillions of dollars to make, as we have only explored a tiny piece of the energy scale so far, and we're pretty sure very interesting stuff happens at higher scales (ultimately, grand unification of all forces). Also, there's a mutual relationship between theory and experiment in physics. The LHC was well motivated by theoretical predictions (most notably the Higgs boson) that needed experimental verification. In physics you have to put your theories to the test, otherwise they're not worth much. Each experimental result is like a nail that fixes a part of your theory space (by excluding possible alternative theories), and that then allows you to explore the space further with greater confidence. Hence the more nails, the better.