I think a very easy solution to prevent no-shows from being an issue (both with people just forgetting to show up, and people purposely doing this to help their clan or allies), would be to just allow spectators to join the AI side after 5 or 10 minutes if someone who signed up didn't show up for battle.
The only way to punish ticket wasting/gear wasting, is to witness it, more admins (or 'junior' admins who only spec) are needed for this to happen.
A thing not directly against your idea, but a problem that would happen:
If you cannot join the AI side of the battle if your faction fight against it, what would hinder you to leave your faction for the time of the battle and rejoin afterwards (either Strategus or ladder clan)?
If something like that was implemented, there would also be a cooldown to join another faction needed.