Thanks, Nick. I do - well sort of. I have a Tusa Geminus mask with bifocal +2.5 diopters. Makes a huge difference, especially when shooting video with my D7000, however, I still miss a lot of the detail on small critters. Although I did "see" some pygmy seahorses in Komodo in August for the first time (other than seeing them through the viewfinder).
Andrew, why not get yourself prescription lenses for your mask? Subject discussed in depth here. I have a Technisub Look 2 with small bifocal lenses, but I'm going to try the company Peter mentioned in the last post of the thread.
Note that I am still able to find lots of cool stuff, I just don't get the full enjoyment until reviewing the photos later.