Honestly July is the HOTTEST time of the year with temps well over 115 on the strip until well into the early morning(i.e. after 2am). The sun doesn't go down until around 8/9pm during the summer here.
I would not recommend going to the Pawn Stars shop in July unless you want to wait in line in the heat for 5 hours to get into a small shop and not see the main stars as they aren't there unless there's filming happening.
My suggestion is to go to the Monte Carlo for the 6pm processional by Blue Man Group through the casino. It's free to watch and something your kids will love(unless they don't like loud noise of course)! I also recommend going to Adventuredome if you have the money, seeing the Bellagio fountains, the Mirage Volcano, and the animatronic show at the Forum Shops at Ceasar's Palace.
Valet is free at all hotels in Vegas but the recommended tip is $1 when you drop it off and $1 on pick up. Remember, these guys are running in the heat of the Vegas summer to get your car to you. Leave yourself PLENTY of time to get from place to place as the strip can be a parking lot sometimes and it can take an hour to go from Circus Circus to anywhere mid-strip even though it's only 4.5 miles long total(think LA freeways at rush hour). The crowds are very high on the weekends in the summer so I would suggest buying tickets for any shows you want to see and making reservations for dinner soon.
Here's a pretty detailed list of all the free things to do in Vegas:
http://www.vegas.com/attractions/free-attractions-las-vegas/
BTW, those cards don't have ACTUAL pornography on them(that's illegal believe it or not) just girls in bikini's.