Well, the Express pass are a LOT better than Fastpass at Disney. You do not have to wait for a return time or anything like that. The TM at the front of each ride will scan the pass and you will be on the ride in roughly 5-10 minutes. The problem with the express pass that you purchase, is that you can only ride each ride ONCE per pass.
So, that leads me to what I would do in your case. You did not mention how many people are traveling, and what hotels are like, so I can help you more when/if you share that information. However, onsite hotel guests at Universal get UNLIMITED express ride access. Just show your room key at each ride, and your on. You can ride the same ride over and over if you like. Also, since you want to do two days at Universal, you can spend ONE night at the hotel, and get TWO days of express.
So, I did some quick pricing for you to give you an idea. Express passes are 55.99 per person, per day. So, I am going to assume it is a family of four. So, for TWO days of express, it will cost you $447.92 before tax. Now, for a hotel, it will only cost $269.00 before tax. This will give your family the same TWO days of express, plus the extra benefit of getting into the HP area an hour before normal guests in the morning, and will also save you gas/time from driving from your current hotel to the parks each day. You will save $178.00 by staying at the hotel. This price was from 7/7-7/8.
Now, if it was just two adults visiting, the price of express would be $224 and the hotel price does not change. So, you save $45 not staying at the hotel this way. However, I would still stay at the hotel becuase of the easy travel back to the hotel, the early entry, and the UNLIMITED express...not to mention the hotels are AMAZING.
Hope this helps and your right, the week of July 4 will be busy and express will be well worth it!