When considering voting for a moderator, is whether they participate notably on the board, on Meta, and on chat important?
TL;DR: I think yes and no.
I don't think it's possible to demonstrate through chat or meta one's potential competence at or particular skill for moderating, or lack thereof. Users may read the chat logs and the meta questions regularly and give to both thoughtful consideration. There are different ways to participate in a community and I would submit that using only one's own context to define acceptable user participation doesn't allow for other valid models. People assign value in different ways and I think it's important to allow for different approaches. Just as in the real world, an online community will have a variety of user roles to choose from. There will be those who are overtly social by hanging in chat and those who ask and answer questions on meta fairly often. Conversely, there will be community members who take a quieter approach to the site. Does that make them a lesser user than the visible extrovert? I think not, personally.
That said, If someone with a rep score of 27 is running for moderator and is presenting himself/herself as very active on the site, I would find that claim to be somewhat mutually exclusive. Perhaps they have a higher rep score on SO or in another SE forum -- as a voter, that's something I would definitely take into consideration as I ponder the candidates. But if someone's only rep score is 27 and the only site they've been active on is Sci-Fi/Fantasy, I would want them to satisfactorily explain to me how I might be able to consider them active on/involved with the site.
Since I'm not running for a moderator position, I did want to defend users who participate in just one topic. I don't think that is necessarily indicative of their overall Sci-Fi/Fantasy experience/knowledge. Like myself, a person might be familiar with and have knowledge of numerous different universes, but not feel quite expert enough to answer the very specific questions that are asked on this forum. Like, I can't tell you what Spock's internal body temperature was in The Wrath of Khan, nor can I tell you how to build an At-At, but I'm familiar with both of these universes, plus many more. A person who is singularly focused could absolutely edit posts for spelling, grammar, and punctuation, have a neutral and unbiased approach to their fellow SE members, have excellent de-escalation and problem-solving skills, and be committed to the vision of the site.