We always leave the auto tips on our account. The people who deliver Room Service are not included in those tips so we tip $2.00-$3.00.
We don't feel that we're expected to tip anyone else extra, but we usually tip our Room Steward, favorite bar waiter, and bartender a little extra at the end of the cruise. This varies depending on the "over and above" service we receive.
There's absolutely no reason to feel guilty about not tipping more than your pre-paid tips.