I'll put in my vote:
"It depends."
Typically, (ooohhh, on the whopping TWO cruises we've been on) the stateroom host, server and assistant server have been outstanding and we have tipped them extra.
But...the head servers have been merely figure heads and did nothing for us other than they stopped at the table for 15 seconds a night to see how things were. We did not require any of their services (what services would they provide anyway?) We had no special requests or celebrations. We tipped them less. (btw, not a TON less, I think we were supposed to tip $11 on the last cruise, we tipped $10)
On this last cruise, we bumped into our server twice on
Castaway Cay. Both times he stopped, asked where the kids were (kids club) asked if we had any questions about CC or we needed help finding anything and chatted for about 5 minutes each time. On the other hand, I was walking to the kids club and our head server was walking toward me---only a couple other people on the path at the time. He looked right at me, looked away and didn't say a word (I'd swear he put his snooty nose in the air, but I can't confirm that) Had he at least stopped and said "hello, how are you?" he MIGHT have earned the standard tip. Go out of your way, stoop down and chat with my kids at the dinner table, impress the kids with a napkin animal....I dunno. Do SOMETHING other than say "everything ok?"
Just my humble $0.02. On the next cruise we'll be celebrating my neice's 21st birthday. If the head server actively participates, we'll tip him better.