You may well find a market for the case. Lot's of people out there that like to build their own computers that run Apple's OS. Many like the idea of modifying an old G5 case because it looks like the early Mac Pros. You may find ads on eBay or Amazon (and, elsewhere) selling the case, innards and all. I don't know the going price but probably more than the computer is worth.
Yes, they are pretty easy to remove. Just some screws and cables to unplug. The drives aren't worth much. Not many people use drives that old due to interface problems. But if you could wipe them, then you might try selling them on eBay. I don't know how inclined you are to doing that sort of stuff.