I know it was my idea, but I've thought of at least one potential counterargument: sometimes you don't want your shields rebuilt. Like in exactly that sort of situation, I might have a CC + a spire civ leader/factory4/fab/other valuable thing that I'm protecting under one or more strong FFs. If the whole thing ends up getting bulldozed over by the AI, once rebuilding I typically will rebuild with no FF, or a weak one at most. If auto-rebuilding exists, now that's actually one more thing I have to remember to do when rebuilding (clear away remains of multiple large FFs or whatever), instead of one less, or else I'll end up dropping lots of resources where I didn't mean to.
That being said, I still think it's worth it overall.