I was thinking something like itunes used to do. you could select several tracks at once and edit all data for them at once. It wasn't very smart but if you wanted to set all the tracks to have the same artist name you could do that.
So, MCDEdit could pop up an MCD values window for the selected set and would write all values that were filled in to all of the selected MCD files, overwriting what was already there. So the user would have to be careful, but I think this would be powerful. I could make a new terrain set and I can set them all to footstep sound "grass" and "fuel: 4" without having to enter those exact same values on dozens of tiles, and then set more specific values for the couple of tiles that might be exceptions to that standard.
Thanks again!