I used to use one keyboard between the two. I didn't really notice much difference beside the fact that command key was the windows key on the keyboard.
You could also look at software like Synergy that allows you to share your keyboard and mouse between multiple machines. I'm not sure how the wacom would work with that though.
I looked at Synergy and a couple of other software solutions. It looks like they require all connected computers to have their own monitors and they have to be in close enough proximity for you to see the (i.e. they share a keyboard and pointing device, but not the monitors).The hardware solution seems like it's a worthwhile investment for me.
Yes, it just depends on what you are looking for. I like to have the computers up side by side so I can compare things between them. If you don't then a KVM is an excellent way to go. Be aware sometimes the usb devices can be a little finicky with the cheap ones.