Worth it? That is definitely going to be a personal value judgement. We went Tuesday of this week. I think the train is the coolest ride in the park and forked over $155 pp for tickets for me and my son and $100 for my husband for a convention 1/2 day 2 p.m. to 6 p.m. park hopper ticket to be able to see it. // Now on my next trip I will skip Universal entirely. If we go to Universal, though, we always do the one day park to park. For us too FYI we can get everything we want to see in both parks done in one day, and there is not enough to do in just one of their parks that we like and think is worth doing.
Do note too this was I'm sure the only time DH will ever go to Universal/IOA (He doesn't like theme parks but was down in Orlando for a three day convention at one of the Universal hotels), he has read all the Harry Potter books and seen all the movies, and DS very much wanted him to see all the HP areas. With him between 3 and 6 p.m., we looked around Diagon Alley, did the train ride from Universal to IOA (the interesting way), had some butter beer and looked around the IOA Harry Potter area, did a tour of the castle, then did the Jurassic Park flume ride and had fun at the Raptor Encounter meet and greet photo area. And I paid $100 for DH to do that.
Morning for me and DS, we did Gringott's (Universal) , the train, Forbidden Journey, the Jurassic Park flume, the Jurassic Park Discovery Center, the new King Kong ride (the only thing we never did before), the Hulk, the spin ride, the free fall ride, (all in Universal) then headed over to IOA and did Despicable me, the Shrek 4D movie, Mummy, Rip Ride Roller Coaster, had lunch -- Then it was 1:30 p.m. we headed back to our hotel to relax and pick up DH and were back again at 3 p.m. and did the items above in the first paragraph. Lots of people like the Spider-Man and Tranformers rides too -- for us it was been there, done that, and bought the T-shirt -- no one in our party had any interest in doing them again. But FYI those are quite popular rides that we skipped and seem to be on most people's to do list. DS also was not interested in seeing any of the shows. DS is 21 and I am in my 50s and DH is in his 60s (party ages could have a bearing on interests).
I am one of those people in the minority too that really hates it that Universal makes it so compelling to do the two parks in one day -- we want to do that or not bother with the parks at all. That makes it super expensive and I'm sure increases their profit margin a lot, as instead of getting around $100 pp from one day people they often get the $155. DS's (21) favorite parks in Orlando are FYI in order (1) SeaWorld, (2) Magic Kingdom, and (3) the Universal/IOA combo. And on our three day trip those were the three we hit.