Four days... Is that three nights? One of which will be taken by Gwen Stefani? Or are you going to multiple nights?
Anyway, I'd stay five days if I were you, just to cover all grounds. The nights are the only currency in Vegasm, really. Only mad dogs and Englishmen go out in the midday sun.
I went to Vegas to see Morrissey a few years ago- certainly worth my while.
I recommend you get a hotel that's a block or two off the strip. The price difference is immense. So is the quality. The cheaper little cupboards on the strip look like a place someone would go to kill a prostitute.
Good luck.