I've been to Hoover dam post 9-11, and they only restricted a couple of areas. It's still an impressive sight to see and very good tour. As far a casinos are concerned, they are the best entertainment value in the USA. You don't need to spend a penny. The strip is the best at night, but it might be a bit chilly this time of year.
My favorites sites that are free:
Luxor - just check the architecture inside & out. The elevators travel at an angle, but they are for guests only.
Bellagio - watch the fountains in the evening, they are incredible. Well maybe more so for the women folk.
Venetian - Checkout the indoor canal in their shopping area.
Ceasars - the shops go on forever, you'll think your lost
Treasure Island - pirate ship battle outdoors. Lot of explosions.
Mirage - Tigers in zoo like setting.
Many of the casinos are interconnected, so you almost never need to go outside except at major intersections. There are free trams between Belliago & the Monte Carlo and between Harrah's and the Mirage. They aren't always easy to find.
Of course there are plenty of attractions that require money, and that's where we usually spend our money. If you are into them, Cirque d sole' and Blue man group are good shows, but are expensive. There are many headliners that pass through Vegas, last time we caught Tim Conway & Harvey Korman and we laugh our heads off.
There is plenty of good food places not too far off the strip, but the Vegas buffet is almost a rite of passage, with the best deals at the older casinos. The fancier the hotel, the fancier the food, the misses & I dropped almost 2 bills for a dinner at the Bellagio. We had to allow 45 minutes so that they could make this dessert that was unbelievable.
Finally, Vegas definitely has some areas that aren't very nice, and I would recommend staying in the strip area, especially if you are not accustomed to cities. The only real annoyance on the strip are the people handing out the adult entertainment books & cards. Just ignore them. They are only tolerated in very limited areas between some of the casinos, so they won't follow you around like they would in some other large cities.
Most of all have fun, and don't try to see everything in one trip, Vegas will still be there the next time you visit.