Visit my parents?
I told them to be like normal Jewish old people and settle in Florida so I could go to the beach in December but no they had to pick the world’s hottest and ugliest place.
I already mantioned the Liberace Museum 
Silenus - you’ve been there too? I agree that it is now one of the best in town, although they have raised their prices recently. Still, would rather see the prices go up than quality go down (the typical way casino buffets go after their opening month).
Back to the OP - there is a lot to do here.
I have really good friends from Illinois - the wife never wanted to come here - her impression of Vegas was a lot of old fat men, smoking cigars playing poker. Granted, you can find that easily, but it is by no means the “new” Las Vegas.
Finally they came to visit - and like a duck to water, she fell in love with Vegas - she discovered shopping, and shows, and great food - plus she won a bit at the slots.
They have come here, at least once a year (sometimes more) ever since.
I have a website with tips and suggestions that might be of interest to you - try the Cheap Thrills page for things to do when you don’t want to spend a lot, or any, money while you are here.
At any rate - just walking the Strip and people watching is usually the most fun of all…you won’t believe what you see just ambling up and down the Strip, on any day, at any time!
Unfortunately, the main two things I went to Vegas for no longer exist! But I really enjoyed the Star Trek Experience and the bungy jumping when I went.
Another thing people do in Vegas is smoke. There’s more people smoking here than anywhere I’ve ever seen, and I’ve been to Paris!
Do all those 3D/4D shows. There’s a couple of things at the big pyramid, and a couple of others I forget exactly where.
Ditto on Red Rocks and Hoover Dam.
I hiked Red Rock Canyon. It was great. I plopped a few photos up here.
Do you like Thai food? Head over to Lotus of Siam.
To echo what other’s have said: The shows. In particular, some of the Cirque du Soleil shows, like “O”, “Mystere”, or “Ka”. Niether my wife nor I drink or gamble, and we’ve gone to Las Vegas just to catch these shows.
Ed
We saw Mystere, and on the way out my boyfriend said, “I think we just saw the pinnacle of human achievement.” What’s more amazing is that they do that twice a day.