Summary: do it if you want to become a career researcher, but if you want to do creative hacking than cut out the middleman and just do it. Gradschool is the hotbed of timewaste and procrastination so don't do it to get yourself focused. If anything, taking some undergrad courses in some topic that is new to you could be much more useful that way.

Even if you want to get into research, leave all ideals and preconceived notions behind. As others have said, doing a phd is depressing as hell. You will have smart people to hang out with every day, but especially if you are thinking of real world applicability of things, you might have a hard time connecting with most of them.