If you're onsite, you have no worries. Really....I'm just back from a stay at RPR and although I could see the crowds, they really didn't impact me at all. Longest wait time was to take a picture of my kid with Jaws.
Specifically the Simpsons....we got there early on day one and walked on. Rode it again later with heavier crowds. Walked on again. Express Pass rocks! Enjoy!