However, I think if everyone in that 38% of the population did vote, it would make a difference, even in those ridings where the results aren't usually close.

It's more like 45% here (and all the way up to 58% in the last provincial election, people here truly do not care), and while I want to believe that's true, that it would make a difference, from what I've seen, even most people who don't give a shit about voting are perfectly happy to blindly go along with the conservative supermajority when pressed. That's pretty anecdotal, though, so who knows?