I've been speaking to an expert on the science of baseball bats recently. They seem to have done a lot more study about the science of baseball than cricket. He was really surprised that low density/big size was considered important for cricket bats and didn't have a ready explanation. If anyone's interested, the state of the art is a book called 'the science of baseball' by A. Terry Bahill. It goes through all the science of how ball/bat collisions work and gives equations for speed of ball on terms of bat weight, ball weight, coefficient of restitution (='pinginess') and the effect of spin on the ball at collision time. All of the results should apply pretty much unaltered for cricket bats, with suitable changes of weight /dimensions etc.
One thing that is neglected in the book is the effect of bat surface friction, and it occurred to me that this could be a significant factor when using a scuff sheet or not, as some scuff sheets are quite smooth and slippery to the ball.