Does one exist? Where? Is there any plans to create one? this would be great.
A guy from BGG created a Yahoo Groups site for something like this, but it doesn’t appear to be very active.
I think most of the people who most want to see something like this overestimate the need. If you really want to learn how to play a game, I don’t think replaying a VASSAL logfile is a very good way to go about it, unless the creator put a lot of time and care into annotating it and recording it with the express purpose of teaching. Given the effort involved, I doubt there are many people out there willing to do it.
On top of that, a logfile should really only be opened with the exact same version of the module that was used to create it, otherwise some features may not work. As time goes on and modules get improved, updated, or overhauled completely, that can render older logfiles unusable.