Adding however much water to improve nose and taste, and diluting from cask strength, are actually two different issues according to a whisky expert I used to hang out with. (A Scot who had a degree in the subject and was employed at the time by Johnnie Walker.)

According to him, the reason whisky is bottled most often at 80-86 proof (40-43% alcohol) is that above around 45% it tends to fry your taste buds and you can't appreciate the complexities so well.

That said, however, if the whisky is in YOUR hand, you can drink it however you darn well please!