It would be outrageous to have a grand piano with a rock band, haha. It would be more practical to have a keyboard, because it's smaller, lighter, easier to set up, and more flexible in sound. But X-Japan had a grand piano, and their drummer Yoshiki played it, but only during solos if I'm not mistaken, he's good but he can't play drums AND the grand piano at the same time haha..
I did learn the piano when I was young, but I gave it up because it was boring and I sucked at it. In fact I hated it. Surprisingly though, when I started learning to play guitars a year ago, my 'background' helped me tremendously. I could play simple scales by ear.
Slowly, though haha.. It also helped me with my tempo, I never had a problem playing at a consistent tempo alone or with a band. I've got many friends with that problem, and they make up for it with tapping their feet, counting in their head, etc.
But one thing.. I wish I told my parents I wanted to learn the guitar and drums instead when I was young, and not cringe in fear at their superiority and just give in. Even later on, I did not want to ask them because I'm afraid they would say "If like piano how? Learn halfway give up". Till today I have not told them I want to formally learn the guitar, but I'm learning myself, buying my own gear, showing that I am serious about it. Heh. My dad did tell me before though, that I should take up a course or something. I told him that I'll think about it 1st haha..