If you opt for Vegas I'd like to make a couple of suggestions,stay at The Flamingo,Bally's and/or Harrah's as all three are closer to the middle.Secondly,forget the bus and cabs and buy a 3 day monorail pass for like $15-$20.The aforementioned casinos may not have all the glitz of others but the monorail will drop you off at the back of most of those and walking through them back to front can be a sightseeing trip on its own.
Also if the mrs doesn't mind hot chicks and great music I highly suggest the X Burlesque show at The Flamingo as I've been three times(once with my mrs) and it's very well done,couples friendly and guaranteed to get someone's motor running.
If that won't work then splurge and definitely take in The Beatles LOVE.