If you're going for precision (and stability), then one thing that stands out to me (one who still has yet to complete his FIRST machine) is that you might have room to widen the spacing between your Z axis rails. Your alignment blocks have space between them and the Z axis trolly. The wider these are, the more stability you 'should' have. If you've got the room to widen them (without widening the outer wooden structure of the Z axis itself), then do it. You don't want to widen the wooden part because that would narrow your Y axis travel.
Just my 2c worth.