Upgrading My TurtleBot: Intel Joule, Raspberry Pi, or Something in Between?

I really enjoy my TurtleBot. I haven't programmed it to do anything very useful, like bringing me coffee, but it's still a lot of fun: It lets even a n00b like me explore and learn a bit about ROS, or Robot Operating System, the influential software platform used by a growing number of robotics researchers and companies around the world. My kids seem to like the TurtleBot, too. It's now decorated with "Frozen" stickers and a drawing of what I assume is Elsa's face. Now, after nearly three years, ElsaBot needs an upgrade.