I feel like my family is rather representative of how families spend time/money at the two parks. We were doing yearly 8-10 day Disney trips with Hoppers, staying onsite, Dining plan, add ons, etc. and bringing Grandma with us for help. We spend so much time at the parks and character dining that have spent about 4 hours total at the resort pool in 4 years. We have never made time for a waterpark there because there is so much to do. We love staying inside the bubble and never have a car, etc. This year we are doing a Universal trip - adults only (just me and my husband) with 4 nights, base tickets, and staying at the holiday inn across the street for $55/night no add ons. I anticipate the bubble feeling so small we may want to leave it. We usually value resort at Disney but I would feel better spending $250/night at Disney for 4-5 people than even $120 at Universal for just 2 people - the space and amenities are more applicable when we have the entire family; when it's just my husband and I, we would prefer to "rough" it to save the money.
As many say, having younger children makes Disney more applicable, and I'm happy to go every year since they forget or experience it so much differently as they age it makes it fun to watch their reactions/preferences change. Older children/adults that go to Universal aren't experiencing it as "new" every year as a child does to Disney. I would be happier taking a small child many times to Disney than a teenager many times to universal. I would want my teen to go do other vacation destinations or even education spots. My kids, 7yo & 3yo (girls) don't know ~85% of the characters at Universal, and they don't know anything that is being added either... they know a little about HP, but only because we had them watch the first movie when we were considering taking them this year. We aren't star wars people either, but that's a small % of Disney. Maybe Disney has less competition in it's age demographics than Universal? Although, I dream of Disney without kids, and intend to retire there (think RV at the campgrounds, not Golden Oaks).
In my mind, Disney is a 7-10 day park for us, and Universal 3-4. After Disney expands/updates, and Universal expands, I think both parks extend the desirable number of days, but do it proportionally. We are in the middle of a 1-3 year Disney break, but by 2021 we will be back often again.
JUST MY THOUGHTS!