All I know is that if my players tried to make glasses that could find true love, the rest of the people at the table would slap them upside the head.
I'll say it again, because I want to know the other side of the argument, and because this was simply not addressed: How is the Wizard supposed to know how to look for something that they don't understand? That's like saying they are going to make a dowsing rod for moon-dust. Even if there's some of it around, they've never touched it or seen it, so how to they know what to key the spell to look for?
True Love (or hope or courage or what not) seem like they are the sorts of things you could look everywhere for, but won't know what you're really looking for until you have experienced it yourself. That is to say, you could find a couple that seems like they are in true love, have one of them punch a WCV, and have nothing happen, because they weren't actually experiencing True Love.
I mean, really, how in the hell can you test for that??