Get tickets to see La Reve at the Wynn. It seriously blew my mind. It is similar to Cirque, but half of it is underwater. There is a pool at the bottom, and there are platforms that rise out of it and then dissapear so the performers dive down into it. The theatre is amazing, it's in a big circle and you really can't get a bad seat (well, actually I would suggest sitting higher up).
http://www.youtube.com/watch?v=Nbl-G...eature=related
The Wynn site was acting wonky, so I didn't link, but I found a short video so you can get an idea. It was outstanding!
We were there recently, DH wanted to see Hoover Dam (I thought it was a snoozefest, but DH wanted to see it). You could do that if that interests you, or do a day trip to see the Grand Canyon if you have never seen it.
We didn't gamble much, either. I like to walk around, see the different hotels. If you've never seen Ceasar's Palace, it's a must see! I am annoyed I didn't walk into the Cosmopolitan... I've been wanting to check it out.
Oh, and hop on the Deuce Bus (actually, if your goal is to do alot of walking around the Vegas.. get a day pass). You can take the Deuce all the way down to Freemont Street (the Old Vegas - where you can see the light show and lots of interesting people watching)
ETA: I just realized you guys are not there for very long... I wouldn't see Grand Canyon then, it will eat up your entire day.
When I went for a short girls' weekend a couple of years ago, we made sure to see one good show, do lots of walking around during the day/hang out at the pool.... and went dancing at night.