This is really hard to interpret properly, because giving the spirits/demons/whatever the attention they're asking for seems to be dangerous (though at this point it's not clear /how/ they're dangerous, aside from wanting to stick to you like a giant leech). So it's basically impossible to be sure if someone is seeing the strong ones and ignoring them for their own self-preservation, or just don't see it at all.
That said, I think there's definitely a stylistic hint about who sees them and who doesn't (aside from their deadpan demeanour, which is actually also a really good hint): whenever things are /shown/ in the panel it seems like there's someone around who can see it, and they're the one who's providing the perspective in that particular scene. So any time we're seeing things from Julia's perspective we can see auras and weak spirits, but not the strong ones; whenever we're seeing things from Miko's perspective we can see all the spirits but not auras, and (I think - I'd need to re-read it to be sure) when we're seeing from Romm's perspective we can see both. The scene in the restaurant was very much like that - Mitsue was clearly aware of the weaker spirits, and when she was the focus (the one doing the exposition) that was what we saw, though I think there were hints that she was aware there may be stronger ones around. Then we switched to Miko's perspective and we could suddenly see /all/ of them.
I'm guessing he assessed Julia based on her not being able to see the strong ones, mostly - that doesn't make much sense, though, since Mitsue (who he obviously has /some/ respect for, even if he's a dick about it) obviously can't see /all/ the strong ones. I doubt his assessment is really accurate - he seems to have a pretty specific idea of what he's looking for, and Julia doesn't fit even though she obviously has /some/ kind of talent.
Really interesting read, though - long slow burn on the plot, but it's definitely progressing and so far at least it's promising to go interesting places.