I've heard a lot about how the grid can use my vehicle's battery for storage and how this will be hugely beneficial for the grid. However, I've never heard anyone explain why I would want to participate.

The grid gets valuable energy storage, adds a bunch of wear to the battery I had to pay for, and I get...?

Demand management is much easier to make a case for and probably much simpler to implement. I get cheaper electricity on my EV charging circuit but the power company gets to turn it on and off. The grid gets demand management, I get cheaper power. I'll still be charged the next day, I don't care that my car was turned off for a couple of hours.