I am anti-car in Vegas. I've been roughly 15 times, always on business. I always stay at a hotel on the strip, and I've never gone far enough away from the Strip to get outside the I-515/215 beltway loop, so if you're expecting to vary from either of these a car might be more welcome. If you cab far away from the Strip to a non-casino or Fremont Street destination for some reason, getting a cab to go back can take a while. That being said, the vast majority of my time is spent along the Strip and for this and any other travel not walkable I've always had very good luck with taxis and the monorail. I like the monorail a lot. The
Las Vegas Monorail runs up and down the Strip and is just pretty handy. The rail stations are toward the backs or sides of the connecting hotels so there's walking involved, but I've found I walk just about as much going to get the car then walking from parking the car when I've had a rental. You can do the valet thing, alternately, but you have to wait for the valet instead of walking which, for me, negates much of the convenience.
You can't hail a cab from the curb typically, but the door of every hotel along the strip has non-stop cab service, so that's handy too. Price-wise it would be hard to project, but convenience-wise I much prefer not having a car.
I will offer this: The first time you see the serpentine line of humanity waiting for a cab to leave the airport, you may want to rethink not renting a car, but this line moves very quickly and it's never been much of a delay. Further, as KingBarkus mentions, the things I like to do in Vegas are 1) eat and 2) drink, not necessarily in that order, so not having to worry about driving is a big, big plus.
My Vegas travel is different from any other travel I do. No matter where else I go, I look for local flavor, non-chain food, unique character in the locale, etc., but Vegas is a place created from whole cloth. The only thing true about the place is the Di Nero line from the movie Casino: "In the end, the house gets it all." Fremont Street is what passes for the historic district, but "historic" should be in air quotes at all times. As recently as the 1950s the place was smaller than today's Tupelo. Las Vegas doesn't build out, it reinvents. The people who live there staff the current iteration. That's why there's nowhere there I care to drive to that's closer than the Grand Canyon. I enjoy it, but it's more theme park than city of the world.