I am very happy with my Canon SD 870 and underwater case and wondering whether to take it a step further and get a wide angle lens. An mount base and wide angle lens would cost almost as much as the underwater case and the camera together. I am not sure if it's worth it for now...

I also not sure about whether I should get a fish-eye lens or a 28mm wide angle lens (which has the advantage of working above water too).

I appreciate any comments,