I am surprised you left a tip. We are never expecting anything, we go into restraunts with an open mind. We have never encountered bad service anywhere at WDW. But we have many times at
Disneyland, and we will pay the bill and we have no problem at all not leaving any tip. If they do not treat us decent I refuse to leave a tip. We were treated horribly at Cafe Orleans in DL back in March. They seated us, and said they were not serving some of the things listed on the menu. (Thats fine) we ordered all salads and waited 45 minutes or longer for them. Then I had to get up and hunt down another waiter for drink refills cause I couldn't find my waiter. Then that was it, he never even offered us a dessert menu. The bill came and I paid exactly what was owed and on the tip line I wrote a big fat 0. That's how we were treated so that's what he got.
Just an observation....if you leave zero for the tip, the waiter isn't likely to realize you were disappointed....instead they'll simply think you were either a foreigner who didn't understand American tipping etiquette, or more likely that you were a cheapskate. When I receive such poor service that I refuse to actually tip, I leave a quarter. This isn't much money for me to be "out"....but it should hopefully make the waiter think "what did I do to deserve only a quarter?" It shows you knew about tipping policy but by leaving something woefully inadequate most servers should know it's because you were unhappy. Or at least that's how it was always done "in my day"....not sure if the young whippersnappers

of today understand.
The other thing you REALLY should have done, was speak to management either during the meal when you were not receiving refills or any attention, or on your way out. If management isn't told there is a problem, then they can't speak with the server to try to correct/retrain on the problem. For the lack of attention on the birthday....that's certainly unfortunate and sad (by the way HAPPY BIRTHDAY), but like others have said, it's not something you can really expect unless you've made prior arrangements (and while I agree the notes on ADR and the acknowledgement at the beginning should have tipped him off) but freebies aren't to be expected. I've not done any birthday celebration in Disney, but when we go to a local restaurant to celebrate, I always talk to the waiter privately (excuse myself for the bathroom and then seek out waiter) and request that they sing for the kids' birthday (hubby would kill me if I did for his, lol). I've never been disappointed and I feel it's because I specifically asked for it. Now, I have had one time when they've come and sang, but brought no treat, and while it was a bit surprising, I realized it was MY expectation that a birthday greeting would include their smallest dessert, but afterwards I realized that no one at the table had ordered dessert, so why should they give it away. After that, I make sure we all order a dessert, and sometimes the birthday dessert will be comped, sometimes I've had them bring the ordered dessert AND whatever little thing they normally offer free for birthdays (making the child VERY happy,

)
I think I'd be most disappointed by the fact that the particular restaurant had a reputation for silly and funny antics and others were getting it and I wasn't. It seems like that restaurant part of what you're going for is the entertainment. So I probably would have mentioned the disappointment to the manager, again so the server could be spoken with about it. No, it wouldn't have changed my experience, but it might change for the next person at his table....and you have to think of that as "if the person before me had complained, maybe my experience would have been different....so I'll pay it forward now in hopes someone else does it for me later". Not perfect, but that's life!