A bit more than a year ago we started redoing every mission in War in Heaven from scratch because...we wanted to, I guess; we decided to start over from a clean slate so we had 100% control of a new approach. After that a few of the missions were again iterated a few times, mostly because the original concepts just didn't pan out into a fun experience.
But by and large we managed to avoid the 'restart the mission' trap, and I think that's down to excellent iterative testing during early development and good pre-design. If the mission gets played to death at every stage of development, you catch problems early. When finished missions didn't live up to the standard of the rest of the campaign we were able to go back and enhance them pretty easily.
Usually the only good reason to redo a mission from scratch is because the concept changes. Crash bugs aren't a great reason to redo a mission - you should haul the file over to Mantis and get it fixed. We solved a lot of SCP bugs that way; just yesterday we found out that is-ai-class...doesn't work, and got it repaired (I think.)
If you have to redo missions from the ground up frequently, though (looking at you, Earth Defense), you're doing something wrong in your development. Something's going wrong in the design and outlining phases that's wasting your time and effort. You should be thinking harder about what each mission is going to be, what gameplay verbs are going to be deployed, what the mission needs to say and do.
By and large FRED is powerful enough that if the fundamental concept hasn't changed you should be able to massage the mission into what you want it to be without restarting. And if you're slick about it it's not hard to retrofit missions; we squeezed major, major features into a few WiH missions very late in the development process because the missions themselves were designed to be modular and expandable.
EDIT: oh and I've used notepad copy and paste to move shared SEXPs and variables between missions before - it's really useful for capship command stuff.