I'm late in thanking the contributors to this thread, but your advice transformed our trip. Thank you all so much! I couldn't figure out how best to split the tickets between Universal and Disney for our 16 day trip, especially with the park reservation system. It would not have been the trip it was without the 14 day tickets for Universal and Disney. Because it was such a busy time in late January and early February, there were days where we hopped from a Disney park to Universal, then to Volcano Bay, or just popped into a park for a couple of hours. We could never have gotten as much done without these tickets, I shudder to think how trapped we might have otherwise been with the crowd levels. It almost felt like having annual passes with so much flexibility. I was initially nervous about it, but we had no issues at all linking the tickets in
MDE and using the physical tickets at Universal. The cost was about what we would have paid for half as much time at each resort if we'd bought the tickets separately from their websites. Our experience with attractiontickets.com was really positive, I hope something similar exists for our next trip.