I came here on a Monday afternoon around 12-1CDT and didn't have any problems navigating the area. The crowd was fairly light. I didn't want to take a tour, just walk on the bridge and take some pictures. I was able to do that. Took about 30 minutes to walk the entire site. It was very windy there and I think that is common weather, so bring a hat or something to keep your head warm.
The dam itself is just a marvel. The sheer size is extraordinary. There isn't really a way to get any perspective on its size from the top, but I hear a trip to the bottom really gives you an idea of how big it is. Best of all, I could walk around FOR FREE!
There is a parking garage at the entrance on the Nevada side that charges $10, but keep driving and you will find free parking. There is another covered parking area that is $10 as well, but I had no trouble finding free parking. You will have to walk further because the pay spots are the closest to the dam, but walk around for an additional 20 minutes to keep those legs loose.