There are 3 World Marks in Vegas, World Mark Spencer Street, World Mark Tropicana and World Mark Las Vegas, the last one being the closest but you're are right about them being a little further away. We'll either drive or take the bus, I wont complain too loudly if its a great deal! :) DH's cousin also said that the resort was so nice that they could have spent a whole day there and not feel like they wasted their trip.
Thanks for all your help ladies! I'm still not sure where we are going to stay but I'm a few steps closer now.