Glenda -Sure, makes perfect sense to play songs in as many keys as possible as an exercise - not to mention if you end up in a band with someone who wants to (can only!) sing Big River in Ab... !!
I'm going to throw in here a gratuitous plug for the Highwaymen (Johnny Cash, Willie Nelson, Waylon Jennings, and Kris Kristofferson). They only made 3 albums (which is still one more than the Traveling Wilburys), but the third in particular (The Road Goes On Forever) is one of my favorite albums. And those four, before they ever got together as a band, were my primary musical influences for MANY years... Nick