It's a good start for sure. I'd guess, and it is just a guess, that a few Dreamers could weaken the barrier just as well as many more normal people. At the very least that's a good starting hypothesis, yeah?

[Applying any sort of science to the Dream Sphere might be counterproductive, but you gotta go about figuring this out somehow, right? Even if 'we can't figure it out' turns out to be the answer, that at least tells you a lot of things it DOESN'T seem to be.]