In my experience, if you engage with CMs and they see that it's your (or someone in your party's) birthday, they'll often do what they can to help. For example, on my brothers birthday last year, we were essentially walked onto three popular rides -- Peter Pan, Soarin' and GOTG. Many CMs enjoy making magic happen for guests and once they have even half a reason to -- such as your being kind or it being your birthday -- they'll do what they can for you. Several times I've simply asked CMs how their day was going and they walked me onto a ride. That's happened at least six times, twice in the last year or so. It often pays to be nice.
As an aside, I try to be kind to everyone. I used to have a grumpy co-worker who didn't talk to many people and seemed rather unhappy with his life. But I'd always say good morning and ask how his weekend was. When he died, he left me a substantial sum of money, quite unexpectedly. Now: I'm not saying be kind to people because they may give you money. What I am saying is that being kind is good for everyone, yourself included. Sometimes it pays off in ways you don't expect. But it always pays off in making me feel good.