I was there in October last year and it was hot, dry and sunny. What is most impressve is that it stays hot until quite late into the night - possibly as a result of all the neon. But the casinos are all climate controlled, so the only thing you need worry about is losing your own cool!
I would seriously recommend trying a little steak restuarant we tried one evening, on the strip, almost opposite the holiday Inn. You can sit out, dine till late and people watch to your hearts content. The food and service are fantastic and at a reasonable price.
Turn up to Vegas on a Monday for the best value hotels and ALWAYS haggle as there are thousands of rooms in hundreds of hotels.
Good luck!