As far as I know anyone can add, at least I can and I didn’t ask for special privileges. I like the ‘honor’ system of it personally, obviously we need to verify everyone’s numbers (even Sauls, nice job btw), but its a good start and builds trust. I believe kevin downloads the spreadsheet so if someone really trashed it he could restore it.
If you have or verify the numbers, I say go for it. I update the stocks I follow, but just started looking at LGIH and don’t feel comfortable doing that one myself.