I'd definitely look into it. Right now I manage to run down my Storm battery in one day of use and am contemplating buying a second standard battery from Verizon.
I don't even think the Storm's battery life is that bad, but I'm always up for an extended battery... especially when you consider the the media capabilities of the Storm. I sold my iPod touch because I plan on using my Storm to listen to music. So yes, an extended battery would be FANTASTIC!