Did You ever refrain from clicking 'This is a great comment' just becase you think that it is not that great, but you still find it valuable? I think that if this hint was 'this is useful comment', I would click it more. Do you have this feeling too or is it just me?
I'm not convinced that we need to soften that language. If the language makes you not want to click, then I say don't. I don't know that we need to encourage zillions of comment upvotes unnecessarily.
In other words, if you think the comment is great, click it. If you don't, don't. If you feel the comment is useful, but not quite up to great standards, but you still want to click it ... Go right ahead. Not gonna hurt anybody in any event. :)
And who knows, your vote might the one which pushes someone into a Pundit badge.