Taking your example of Yelp. I want to be able to filter out (personalize) my overall reviews by being able to flag reviews I think are ridiculous (such as 1 star ratings base on other loud customers that may not have anything to do with the restaurant or food they are reviewing). I would also like to dive in deeper on reviews such as reviewing specific dishes, viewing full menus online, etc...
Emotions don't tell me how a particular dish tastes. It doesn't tell me why someone reacted the way they rated the restaurant (or whatever). Personally, the collective emotions idea doesn't solve anything for me.
Your data set is too small for people to yet understand why they should be using it.
Determining the mood from tweets and linking that mood to the keywords in the tweet - that would be interesting and patterns would start to emerge immediately.