While I'm a HUGE DL person, going for only day is pretty expensive ($115-119 per person, depending on the day, for every person 10yo+, and $99 for each child 3-9yo)... Plus more if you want to visit both parks. If you had 2-3 days to go, I'd wholly recommend it. But, for essentially a partial day (leaving SD at 6:00am would mean DL by 8:30ish, going solid for 12 hours maybe [on a day it will likely be open 8am-12am], back in the car, and be back to SD by 11pm-ish), it seems a bit spendy.
Looking at it from a purely financial standpoint, let's assume you'd be going on a weekend or "peak" day. For ease, let's assume a family of 4: 2 adults, and 2 kids, one over 10 and 1 under 10. So, for one day, that would be $454 for admission. It's a fair bet that the park would be open 8am-12am, so 16 hours. $454 divided by 16 hour operating day equals $28.38 per hour. However, if you cut your day short, let's say 12 hours, it's $37.83 per hour. 9 hours? $50.44 per hour. And that's not considering food (hot dog meal is $7 for hot dog and chips or apples, and another $3.69 for a soda, or $42.76 for a family of 4; and that's one of the cheapest meals they sell!)...
--Mimi
Mom to Lala (2004), Bonus Mom to Big Sis 1 (1991) and Big Sis 2 (1992)
Grammy to Big Kindy Kid (2011), Big Pre-K Kid (2012),
Grandbaby Appendage (2014), and New Baby Grandboy (summer 2017)