A "Like" button/system is better than "Thanks"
Good point. Let's have some time, and there will come something else probably ;)
I think "Thanks" there just stand for "Yes" in "liking". Liking adds "no", which is more obvious way to rate the content basing on visitors votes.
I personally "like" it and can't deny something like this could work well as the miniBB add-on. But I'm considering to put it not just for miniBB messages, but for the whole forums and may be even for any standalone web-page, which would allow to completely control voting on any part of your content. If such add-on would be easy to set-up and overview, it would be great, and would deserve a good price ;)