It can make a difference if you put the time in. It can also pay off in more than just money.
I'm also an extreme introvert. We had an elderly couple who took a liking to me, and became my first regulars. I grew less and less shy the more they came in.
They showed up shortly before Christmas one year with cards for me and my family and a gift for my son. I couldn't believe they had even thought about my quiet ass.
Sure the money was nice, but I was absolutely floored by this gesture. I was at a loss for words (which I usually am anyway) but the relationship I had built with these guests ended up meaning more to me than their generous tip.