We have had things like that in the past but they really didn't help much. What ended up happening was people would just Like a comment and then someone else would and someone else... and there was no discussion. Some folks put a lot of effort into making a post and it's quite disheartening to see that no one has responded to it.
By not having simple likes we encourage people to respond, even if it is just a smiley or a "That's really cool" type post.
We may consider Likes again in the future as times change, but that was the result the last two times we tried it.
I agree that a Like is a great feature, it just unfortunately discourages discussion, which is the opposite of what a forum is all about.
Def