I remember a columnist opining that when doing the national anthem, the best option was to do it straight ahead, not draw it out, and not to dress it up with alternate flourishes. In other words, just deliver it and get done.
I'm generally in agreement with that approach. You're there to serve a function, not to show off your musical chops and prove what a stud / studette you are. There's no real reason to draw it out and improvise.
I thought Alicia Keys' version strained this rule pretty far, but I did think she was tasteful and I generally liked what she did. I thought she could easily have sped it up and gotten through it faster.