1) Unfortunately, WDW does very little for birthdays or other special days.
2) They simply do not have the staff or time.
3) Characters can't spend extra time, or other people will be upset.
4) With over 15,000,000 visitors, there are "special" days for lots of people.
5) Sometimes they try a lot, and other times they don't try at all.
6) All depends upon the CM at the time and place.
7) If you want something special, you need to buy it (ie, special cake)
8) What you "might" get at eateries
. . . birthday wish from the CM's
. . . birthday nod from the characters (non-face-characters can't talk)
. . . table sprinkled with confetti
. . . card signed by characters
. . . cupcake with a candle, except at AK and AKL
. . . nothing