I'll be down in Vegas during the long weekend of August too!
For sure b/c it was nearly 50 degrees in Vegas last week, it's fine to walk around the streets w/ a husband-beater on.
And like what SkinnyPupp said, don't go to clubs wearing what you wore during the day. Especially when you're going clubbing w/ a group of guys, it's harder to get in.
Have fun and dress up