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Disneyland Forum! We love helping WDW vets visiting DLR for the first time.
How many people and what are the ages of the people in your party?
Are your two days before or after your runs? That might impact how much you can get done. While the park hours haven't been posted yet, Disneyland is usually open from 8 am - 11 pm or midnight and DCA from 8 am - 9 pm or 10 pm. Assuming that you aren't tired from a morning race or going to bed early to get up for a race the next morning, the longer park hours give you a lot more time to experience DLR than what you have had at WDW. While there are only two parks, together they have close to the same number of rides as all four parks at WDW.
Personally, I feel that LL is more valuable at DLR than at WDW. At DLR, you don't book any LL attractions in advance. Once everyone in your group has passed the entrance turnstile, you can book your first attraction. After that, you can book another attraction every two hours, or after you used one of your LL. There are several threads on how to get the most out of LL. If you are interested, I can provide links.
DCA was originally Disneyland's parking lot so the two are very close. In fact, you'll run through both during any of the Run Disney courses. I think the estimate I read was that it is 250 feet from turnstile to turnstile. Lunar New Year is a very popular festival at DCA. It usually takes place from mid January to mid February and includes food booths, activities and a special processional. You could do one day at each park or you could do one full day at Disneyland plus a park hopper day for DCA and DL.
Regarding shows - Disneyland should have Paint the Night, Fantasmic, fireworks, Fire of the Rising Moon/Shadows of Memory & Tapestry of Happiness. I'm not sure how much of the 70th celebration will return that early in the year. They may also have the 70th daytime cavalcade. DCA should have World of Color: Happiness and possibly a Lunar New Year processional. I say possibly because there is quite a bit of backstage construction at DCA and it may impact the parades. Construction is part of the reason RunDisney won't be returning to Disneyland for a while.
@BrianL do you have an updated list of ride comparisons between DLR and WDW?