It is still the fastest-growing city in the U.S., but there's a big limit to how much it can grow in the future, being in a valley. I flew home on the red-eye the last time I was there, and looking out the window, it's really striking how the lights just suddenly end at the mountains. It also has no decent-sized surrounding towns that would help make it a larger market.
I was surprised to learn that Las Vegas-Paradise-Pahrump is now the 25th largest combined statistical area in the U.S., though.
As for the sports betting issue, the easy solution is simply to take any games involving the local team off the board. That what the casinos currently do whenever UNLV plays in college football and basketball. The stigma comes mostly from the days when a lot of the casinos had mob ties, which is no longer the case. The casinos are very diligent about making sure things are above board. With all the money the casinos now make legitimately, they don't want there to be even a hint of funny business.