Just my two cents, because I hate paying for things that I'm already paying to see: Paying for Express Pass is a waste of money.

Although it can possibly be justified on an extremely busy day (I've unfortunately been to a few, where every single standby except Shrek is over an hour, bigger rides three hours or so), but the price is also as much as the park tickets themselves on such days. Also, you'll end up spending time waiting in line anyways because so many people also bought the Express Pass, so you're basically paying an outrageous amount of money to wait 20-30 minutes instead of over an hour on those extremely busy days. To be honest, on those days it's best to just not go at all. Of course you probably won't know it's like that until that day, but I wouldn't do more damage to your wallet by throwing even more money at Universal. If it's like that, I say relax and wait in those extremely long lines. It's not worth throwing $70 plus for each person to have an Express Pass on top of the park ticket (IMO).

The best way to pay for Universal Express is to stay at their hotels, as others have noted. It's only for a part of the day (after 4pm, I believe), but it's completely worth it if it's busier. You can hit up the parks in the morning (which you'll probably get early access to) with a few standby waits, chill at the hotel until 4pm, then hit up the parks again. If you do this though, avoid Minion Mayhem at 4pm, everyone seems to go there all at once and you'll spend time waiting when you really shouldn't have to.

On most days though, if you are there for a full day, you should be able to do pretty much every major attraction in a single day without Express Pass. I've done this many times, so I speak from experience and usually go on a few rides twice.