Gaming is for having fun. Fun requires clear rules.
Loosing the area won't get you the token back in your hand, it will send it to the pool from which you draw your power tokens when gaining them.
Yes, of course. I didn't say it clearly. It's the only way to send it back to the pool and later earn it.
Waiting until next turn might be a poor decision if a card comes up that would have benefitted you had you held that area - it can make the power token well worth spending.
Yes, it can. But spending power token on area that has only crown for 1 turn is pointless. Also sometimes it's true with alone castle (when you have many troops and it can deceive your enemies that you are not so strong). I think barrel is always worth.
As I said you have to think about spending power token, especially when you plan to return next turn.