Great, I don't think I'm articulating the problems I see with it well enough possibly.
We have already established that people that know how to play well, are already going to be playing well without directly saying it, so they are just going to go about their daily business.
So the question is, how do you get people that are not playing well to want to get better? You mention the bonus, but what does that entail? We both agree that there are quite a few bonuses in the game, which kind of nullifies the impact or importance of yet another. I still don't see how it encourages people to play better or do more. I just don't see the "hook".
A daily rank system of some sort that shows the average of Today's best players scores with in your current roll, in that content with no names only scores and roll, or perhaps the average score of those rolls for that given day perhaps, weekly maybe? This coupled with the help text you mentioned to explain how to improve in that roll, how to improve your score in that text etc.. So that people question "whoa how did they get a score of 500! that's crazy I only got 120" or w/e Just an example of something that could "hook" people into wanting to be better. Something akin to the time completed on dungeon thing. You wouldn't want to show everyone the score, just see your own, so you don't end up in a situation where people bombard a bad player more so than they already are bombarded.
I don't know I'm just throwing stuff out there to help you improve your suggestion.