Wave is literally a Wiki-IM hybrid.
The valuable part of a wiki IMHO, is that the consensus, or at least the representative views, generally float to the top. All the history is there for the curious, but it's mostly archival. If waves allow consensus, conclusions, structure, and action items to "float to the top", and typos, mis-statements, and rejected viewpoints to sink, then I see much hope in Google Wave. I realize some kind of editing, possibly with the aid of plugins, is required to achieve this goal, but the point is how easily the final "document" can be extracted from the wave process.