The dining plan -- in one version or another has been around since at least the early 1990s. With the popularity of the plan, I suspect it won't be heading out to pasture... Sure, it may get a few more changes as Disney continues to "improve" its efficiencies, but I will have to assume that it's not going to go away.
I was assuming that the OP couldn't get the plan for '06 because they were using some other room discount (or were staying off-property).