It’s a nice idea in theory. In reality, the “thumbs up” system often doesn’t work too well. The best example of this was one highly rated comment that I noticed on YouTube:
“Can I get thumbs up for no reason?”
For sure, F1F community would not fall that low but I still see some risks:
1) The quality of arguments would often be ignored when rating comments. I guess we all have seen comments on other sites where the arguments are totally rubbish (and which obviously do not belong to “well said” and “funny” categories either) but are still highly rated just because most “evaluators” like the politician / the driver / anyone or anything else that is praised in the comment.
2) People might start paying more attention to the anticipated popularity of their comments instead of expressing their real opinions
3) There could be more agressive and radical comments as they are the ones, which attract more attention
4) It’s definitely easier to put a “+”/”-” than justify and defend your opinion in writing
These are the reasons why I believe that the quality of the site would suffer if “thumbs up” system was implemented. I believe COTD and the option to reply to the comments is enough. And now we also have the option to write a personal message like “Hey, I love your comment about [...], well said.”
So I agree with matt90, David, ed24f1 and slr :)