South Point offers free shuttle to and from McCarran. You really don't need a car unless you plan on doing some sight seeing. SP is about 8 miles or so south of the Mandalay Bay/ Center Strip. There will be plenty of people there with cars you can catch a ride with. The only off premises activity is the Chipboard Get Together at the Plams. If it will be there or not this year I don't know. People always car pool. So a car is up to you.
Barry