If these extreme emotions are indeed useful, then maybe we should look to explicitly seek them out (depending on whether we think we're below the optimal level of the emotion in question).

• To generate the ups, maybe it'd be a good idea to hang out with friends, get drunk, and dream about ambitious ideas. Only focusing on the happy paths. Well, people already do this but I guess my point is that maybe it should be done more often and more explicitly.
• I'm not sure how the downs would be generated.

Thoughts on the usefulness of these emotions:

• I agree that the ups are useful (motivation, communicate your excitement...). There are downsides like overconfidence, but I think these downsides are usually outweighed by the benefits.
• As for the downs, my impression is that a lot of the time it just makes people lethargic and doesn't really motivate change. But then there are times when they do motivate change. It seems that people experience more than the optimal level of "downs". You could make the point that this is because people don't handle the downs well, but even if they were better handled I'm still bearish on the value of downs.
• (I spent over a year working on a startup that failed and went through these emotions.)

To anyone who hasn't seen it, Inside Out is a movie that is relevant to this talk about the usefulness of "ups" and "downs".