I understand tags, dispositions, and cues as having roleplaying benefits and meta-mechanical benefits. Page 35 talks about earning Plot Points for "particularly good Narrations" and I take this to mean staying in character, using cues, enhancing the excitement, etc.
I give Plot Points to my players for all of those as long as they have meaning. Just because someone says, "I'd buy THAT for a dollar!" all the time, doesn't mean they are getting a Plot Point for it.
I have also started using a rule where, if NONE of the players play a Plot Point during the Turn, I get one at the end of the Turn anyways. That way they cannot meta-starve the GM and it encourages creative use.