I had several of the Intensity Series on VHS and I converted them, and bought the remaining ones, on DVD. I've never regretted it; the DVDs are awesome. The premixes are good, not as extensive as in Body Blast, but good non-the-less. I only just started using the mix and max feature, but I've already found it to be a useful tool.
I'd switch if I were you. I traded all my Cathe VHS tapes over at Videofitness, by the way.
Shelbygirl