It's the cost of doing business - it depends a lot on the caliber of the restaurant of course, but if you can't afford 20% you may do better to stay home. Maybe I'm spoiled after over three decades of work experience in high-end dining atmospheres; just remember the rules of supply and demand.
There is always someone willing to tip 30% for the same experience. The valet, maitre' d, sommelier (as in my case) are often part of the formula.
Do I have some stories...
It makes a difference. Believe it, I know.