At Noodles: You've already named the great things that Late Night has to offer:
+ Instruments. I'd really love to have the piano etc.!
+ Vampires.
+ New items / hair / clothes.
(+ Butlers.)
But please keep in mind that the butler loves cooking to much, and will do that all the day, making your own sims stop what they where doing and going to eat, if they are hungry or not.
My way to prevent this is to made the door to the kitchen 'Only accable for family' so no other people can pass that door, including buttlers.
They can be an extra chat, for incase social is getting low and they do the laundry. If they have a hidden trait I don't know. I hope they do, but I'm not sure. When you find out, please let me know.