I held off updating for a while since some mods were not yet updated (and still aren't). And I had some ships turning up underground (a couple rovers so far...haven't checked everything yet)...so I moved them to safer locations in 0.19 and tried updating the save again. For a couple things that have parts that haven't been updated (damned robotics hinges) I made replacement craft and edited them into the save in place of the others. My biggest problem was all the Dishy JEB 9000 units that I have attached to ships spread all over the solar system...but I used the new Dishy Bill 9000 cfg file in place of the old JEB 9000 cfg file, with edits, and all of the old units now link to MechJeb 2. So, yes... A bother to maintain big projects, but doable.