On the invisible deck, there is absolutely no reason to spend your money on a DVD.
I'm going to politely disagree as there have been some very nice DVDs that explore the possibilities of the gimmick. Jay Sankey's Invisible for example is one of his better works.
I know it sounds like I **** on DVDs a lot, but only because so many of them are crap. While Jay's work tends to be hit-and-miss, his compilation DVDs are actually some of his strongest works.