FWIW, I recently ordered a new genoa. In talking with the sailmaker about clew height -- I was interested in a higher clew, for exactly the reasons people suggest here; thanks again for all the advice on this board -- I commented that I was happy to trade off sail area for visibility and less possible issue in any seas. His response was that sail area actually increases as you raise the clew, due to the geometry of the triangle.
Since I wanted the high clew regardless, I will admit to not having bothered to work the trigonometry myself and just depending on his (well established) reputation for knowing his business, but I pass the comment on here. It seems that maybe the issue with a low clew has more to do with where the sail area is, and putting it down by the foot of the genoa, than actually increasing total sail area.
I know racers like low clews, so there must be some performance benefit to having them, but whatever it is may not actually be more total sail area.