Every time that I have driven through Vegas to/from school, I have seen quite a bit of traffic going by, and that was just from the highway! I never once stopped, but always saw something. Most recently back at the beginning of June I saw a ton of flights of F-15s and a few flights of F-16s coming in. Also some C-130 action too. It's a very busy base relative to other bases, since it is such a huge training facility, and not just for the USAF. I'd say you have a fair chance of seeing some action by just being in the vicinity.
Boilerup! Go Purdue!