Calculation and visualisation exercises - do they work? I would like input from actual experience of improving calculation and visualization: can anyone testify to achieving actual and significant improvement in ability to calculate and visualize as a result of deliberately doing exercises set to train this skill? If so, if you could describe the delta of improvement (before, after), and the time it took, that would be appreciated.

My own definition of significant improvement would mean going from missing move possibilities that lie 4-5 moves down the road, to actually seeing them as almost as easily as if the position was on the board now.
My performance rating was four to five hundred points above my actual rating in tournaments where I prepared primarily with calculation/visualization exercises; while tournaments without tactical training showed a performance rating closer to actual.
So, I would say these exercises definitely make you sharper.  There are permanent gains over time but I think you have to continue to use the ability or it will atrophy to some extent.