In addition to the above-mentioned joys of
DCL, we find we like the style of the ship. It's very classical and feels like a ship more than many of the other lines, which feel more like a Vegas hotel on the sea. When I am on DCL, I feel pure bliss. It just clicks for me - even though I don't really care about character interactions or most of the shows. It's more about the vibe of the ship itself, the service, and the cleanliness.
One thing that might help you decide is how you do WDW. Do you stay on property at one of the nicer hotels and find the cost worth it? Or do you do the off-site hotels because the extra cost is a waste in your mind? To me, sailing DCL is somewhat similar. If you want to be surrounded by super-clean, well-styled, Disney day and night, you pay for it. But, if you are less concerned with that as the actual activities and ports, then it isn't worth the extra cost. Maybe its not a perfect analogy, but it might help. We tend to splurge on trips to stay at the more expensive hotels (actually usually only do moderate at WDW because we have one we love that feels close to a deluxe to us), because we really like being in the nicer setting the entire trip. But we are also lower energy people, not really looking for thrills and more concerned with relaxing and comfort.
That said, we have limited experience with other lines, from long long ago, and might be surprised how much we like them now days - we are branching out in the next couple of years to experiment.
From what you describe and in your responses, I have the sense that the extra money might not be worth it to you, particularly if you are the type that will be looking for whether you got your money's worth the entire cruise. It's easy to pick apart Disney's premium cost if that is the mindset you have going in. But only you know yourself well. I would watch lots of
YouTube vlogs of both lines and I think it will become pretty obvious if it is worth the extra cost to you.