If it's unknown in advance surely it's more rational to spread the research out instead of putting most of the available eggs in a single basket.

CERN found Higgs - which was proposed decades before CERN was built. There is nothing like the Higgs proposal around today.

That's the real problem. Spend $20bn on some new models, and then you can spend $20bn chasing the most interesting prospects.

That's far more likely to get you somewhere exciting than the experimental equivalent of throwing more spaghetti at the wall and hoping some of it does something unexpected.