This may sound obvious, but...
When you go out to eat, you buy into this system and you essentially owe the server wages. "The worker is worth his wages." as Jesus says in Luke 10:7.
Christ wanted the hallmark of His followers to be love. Love, in this context, is generosity. We want servers to associate Christians with real ten dollar bills, not these.
Think of it this way -
Everyone ought to tip sufficiently. Christians who want to show love have an opportunity to tip abudantly.
For a few more dollars, you can make your server's night better. Why not do it?
Personally I tend to think of 20% as a baseline and go up from there for good service. Perhaps because I was a server once and I know how difficult it is.
And for those of you who are generous, keep it up.
#1 There are wonderful places to eat that don't require table service - if that's what your budget allows, then do it - my personal favorite: black bean soup and bread bowl here.
Could there be a theological disconnect on a deeper level when it comes to tipping? I think yes, and I agree with Karen Swallow Prior's assessment.
Worth noting, even the makers of the fake money tracts, Make It Clear Ministries, encourages patrons not to leave their fake money tracts as tips.
I realize that small amounts add up over a month or a year. But I think, given the same amount of money, you should go out to eat 9 times and tip well rather than go out to eat 10 times and tip poorly.
By "camp out" I mean to sit at a table for long stretches of time without ordering food or drinks. (Unfortunately, this is a favorite of church groups in my experience.)