In my experience, the number of "significant scientific researchers" is rather small. If you happen to have some of them in-country already, great! Fund them so they'll stay. If you can poach them from outside the country, it's going to take money to get them set up and going. Increasing the number of researchers in a particular place will have a magnification effect, drawing students, p-docs and the like. And it provides continuity given that such researchers are at various stages of their career.

Researchers prefer to have similar-minded people to talk to, so multi-person setups will be preferred (all things equal). Experimental research can be (real) expensive, which is another reason to clump the researchers.