Whenever I visit Vegas, I always check the exhibits at the Bellagio Gallery. They have rotating exhibits from various collections, so there's always something different from year to year. I've seen everything from Rembrandts to Monets to Egyptian Sarcophagi.
When you plan your Vegas visit, check the Bellagio Gallery website and see if there's an exhibit that interests you.
Tip: It's a jaunt down a long hallway to get to the gallery, passing Cafe Gelato, which has many flavorful selections of Gelato, including some sugar-free selections. Although food is generally prohibited in the museum, it's a nice side-stop to grab a snack.
Tip: Photos are generally prohibited in the museum. Leave your cameras in your car and your phones in your pocket.
Tip: For the artistic type people, bring a small notebook and pen to jot down notes on your observations. Seeing the work of masters can inspire you to jot down notes helpful with your own work.
Tip: Pay the extra few bucks (if required) to get the magic audio wands that explain the background story on each artistic work. It's fascinating to hear about the artist and his/her reason or influence for creating the particular work.