The only thing that drove us mad during a late July trip was the large tour groups that tend to visit during that type of the year. We tried our best to steer clear of them, but sometimes we couldn't. Luckily on several occasions, awesome CM's helped us out when we would get "swept up in the sea of a group".
That being said, any summer trip is going to be super hot. We make sure to take mid-day breaks to be out of the heat during peak sunshine. We enjoy the parks at night during the summer because the sun is down.
Make sure to hydrate yourself at all times. Also we found Frogg Toggs to provide relief in the heat.
For shoes, we would have died if we wore sneakers. Instead, we wear Keens sandals, which are great because they dry really fast after getting wet and your feet don't slide around in them.
DO NOT forget sunscreen. It's a must.