As a wife who gets "taken" to Vegas at least twice a year by her hubby, here's my ideal itinerary:
Fly in at night so you can see the lights of the strip as you arrive. Arrange to have limo pick you up at airport -- it's Vegas! Splurge a little! A room at Mirage or a suite at Caesar's. Days spent poolside or shopping at Caesar's or the Venetian -- hey, somebody's gotta spend those winnings, am I right? See a different show every night -- I see Danny Gans every time I go to Vegas! He's a doll! Hit the breakfast buffet at Bellagio and don't forget to look at the amazing glass sculpture in the lobby. It will take your breath away.
I'll be in Vegas with my hubby in April, ta ta!

My girlfriend and I spent our 5 year anniversary at Bellagio and LOVED IT. YOU ARE GOING TO HAVE SUCH A GREAT TIME. You couldn't have picked a better hotel. For a good dinner, go to Lawry's. We had an awesome steak there. And for the shows - I recommend "O". Truly spectacular. Take the advice of the other posting - walk down the strip and see the fountains, the volcano, and the pirate show.