Re: Worker
The worker is useful as defense/support throughout the entire game. If you keep gathering resources (particularly wood) even after everything is upgraded, you will be able to rebuild doors and stuff when they get broken. Repairing your castle doors costs resources. If you've ever tried to rebuild a door and nothing was happening--it's because you have no resources to fix it with!
Having a good stash of resources even after everything is upgraded makes defending go smoother.
The upgraded bombs also work quite well for defense. I managed to take on one upgraded warrior with my own worker by myself yesterday, dodging his lunging attacks and chucking bombs during his 'recovery'. I'm sure he was cursing