I think (and I'm by far no particle physicists) that generally the larger the collider, the better the results can be. Also allows for more energetic collisions with potential discovery of new particles.
Particle physicists had their chance on trying prove the existence of any new particles with CERN and their newest project but ultimately they failed to discover any. First, it's too costly. Second, their theory on bridging the major two theories (relativity and quantum physics) with the assumably new particles is simply too complicated that involves a lot of constants compared to other theory models. There are better way to advance the progress of academic physics, but building a new collider would not help.
I would like to understand how the size/capability of this proposed facility compares to both CERN and also the never completed Superconducting Supercollider. I will never get over the fact that, as Americans, we could have had a huge lead in this research. We started to build it, then decided to stop.
