My niece went on the March Break. And said when she went on rides not included in her Express Pass (purchased, not hotel), the wait was insane. And she wishes she had purchased VIP?? instead.
She mentioned that the difference between the two choices was not that great. As Express was already a hefty add-on.
But this was a one day visit.
But besides talking about the insane crowds, she did Disney on the same trip so it was a comparable, she had a great time.
And her eldest (10) and the adults loved the roller coasters.
Two pieces of good news for the OP here: One, March break is far more crowded than the last half of August. And two, fortunately only two major attractions do not have EP - Hagrid and Velocicoaster.
Those are both must do IMHO. And doable fairly easily in August, with a little planning. To date, when Hagrid is very busy, they switch to a virtual line with assigned times - so no need to wait physically in line for hours. Never used it myself, as it simply was not crowded enough last August for it to kick in.
Assuming that holds this year for the OP, the strategy is to high tail it to those rides at rope drop, or hit them just before close. Hagrid has the longer, slower line; we rode it multiple times (beginning or end of day) with waits between 20-40 minutes. VC was much easier - one day we got there right after open, and got three rides in under 30 minutes. Which, frankly, at my age first thing in the morning is quite enough.
Another bit of "insider" advice for the OP I do not think I have mentioned - if early entry for resort guests is at just one park - ie either IOA or Studios only, not both -
avoid the one with early admission. Instead, head to the other one and get in line 30 minutes before the scheduled open. You'll find almost everyone will head to the the park with EE, and most days the gates open at least a few minutes early.
This works best with the current line up if the Studios have EE. For example - our trip last August. The Studios had early entry all week - 8AM. IOA scheduled to open at 9. We had the unlimited EPs with our stay at Royal Pacific, but IOA has the two rides without EPs. So first day we queued up around 8:30, with just a few people ahead of us (they have multiple gates to line up at, all in a row). Let us in about 8:50; we walked quickly to VC, and kept walking right on to the ride.
This strategy works for those with or without EPs; as those who have EPs almost always target those rides first (cause they're not worried about lining up for anything else), you would think those without express would perhaps take advantage of that and hit the other big attractions instead first thing, with the EP crowds all running to the back of the park. But people being people, it seems almost
everyone makes a beeline for those two at open.
There are those that will head to Studios during EE, and if they have park-to-park get on the first Hoqsmeade train to IOA, which lets you off right beside Hagrids. But it seems the train doesn't allow boarding until 9AM, meaning the earliest you will arrive on the other side is probably 9:10-9:15. And by then lots of rope drop people are already in line.
Hope I'm not getting too technical here. I think the bottom line is, with a stay that long that time of year there is indeed little need for planning. Use the early entry for Volcano Bay, rope drop the other parks and hit the Harry Potter areas plus VC first .... and I think you're golden.
My only other recommendation - we've tried all the pools at Universal aside from Endless Summer. CB's is great - most are. But if you're going to hop over to try another one just once, I'd suggest the Hard Rock. Probably the liveliest pool - maybe too much of a party atmosphere for some if it's late at night - but great for kids and teens during the day.