With EP, the only thing you need to worry about is HP. With the exception of HP, Universal has never felt crowded to me in way that Disney has. I've never had to push my way through wall to wall people or felt overcrowded in the park even during busy times.
Now HP is another story. It is always crowded, even in the off season it is packed. My tolerance for crowds is nonexistent. You start putting 4 or 5 people in those little shops, and I'm out of there. They are very small.
However, if you are early morning people or willing to get up, you will be fine. You will actually probably have better luck with touring HP on high crowd days than if you were going on a low crowd day. That has been my experience. My best / least crowded HP trip was July last year. Here's the reason why.
When the parks aren't as crowded, they open at 9, early entry is at 8, not too early. People don't seem to have too much trouble making it to the parks between 8:30 and 9:30, so you see larger crowds almost right from the start. If you are outside the gates 30 minutes before opening, you may see a good 30 minutes from 8 to 8:30 that are relatively uncrowned due to people still making their way into the park, but by 9 the HP section will start feeling a little crowded, and only get worse as the day goes on. I'm not saying the lines will be ridiculously long or anything, just that the streets and shops will start filling up with people. It doesn't take a large number to crowd the small stores. Uni also only gives you access to one park early normally.
However, when the parks are forecasted to be at very high crowd levels, early entry can be as early as 7:00, meaning be standing outside the gates by 6:30, leave the room by 6, get up at 5 / 5:30 to get ready. People are lazy, they don't want to get up that early on vacation. So, if you are willing to get up, you can get some good touring in while everybody else is still in bed. Instead of 30 minutes, you gain anywhere from 1.5 to 2.5 hrs of relatively uncrowded touring as people are still going to start showing up around 8:30 to 9:30.
The second benefit to the high crowds is that Universal will open both parks for early entry instead of only one. At least they did last year. This disperses the already thinned out crowd across two parks which helps as well.
You should have no problem touring each park early a different morning. Stay until the crowds get to be too much for you, and then move on to the rest of the park using your EP to avoid lines. My advice is hit the stores and spell spots first. Then as crowds begin to pick up, hit the tour only queues. Have a late brunch or early lunch and then leave for a different part of the park. The streets and shops in the rest of the park won't be anywhere near as crowded as the HP sections, so you should be ok.
If the parks are open late, you may also have luck returning at night with minimal crowds. This is iffy however because even when Uni stays open late, late is usually 9 or 10 which isn't very late to most people, so it doesn't necessarily always thin the crowds out. When the parks close at 6 or 7 it's even worse. But many people have reported lower wait times at night.
