Are you traveling with kids? If so, what are their ages?
In general, I consider DCA much less fun than DL. I love things about it but there just isn't enough for me, an older adult with no kids along, to want to spend a whole day there. They've also removed some of my favorite things, in particular, the musical shows that used to play in the big theater (Aladdin and Frozen). They briefly brought back a scaled-down production (Rogers the Musical) but there has been nothing there for ages now and I've not heard of any plans for it going forward, which is a huge shame.
Carsland is cute but I don't spend much time there. I don't have much interest in it, though I think Radiator Springs Racers is wonderful. In general, CL is geared to younger kids and their parents. I can appreciate the detail and the excellence of the Imagineers who created it but there's not much I like to DO when I'm there.
Also don't go in the back part of DCA where the "carnival" rides and younger kid things are. In general, I don't find a lot to do in DCA except for dining and strolling and a couple of rides I love.
If you have younger kids, though, it's a great place! Redwood Creek Trail is awesome, and the short parades & general atmosphere is pretty cool for kids. It's also good for a day if you've never been there before.
Anyway, I feel like DL itself has so much for everyone that I wouldn't dedicate a lot of time to DCA. If you have hoppers, then you can check it out or go over and do something in particular without having to stay all day. Otherwise, I'd echo what others have said and use most of your days for DL.
And the suggestion to be sure and check ahead about after-hours events is a great one, as that can be an unpleasant surprise if you have a 1-park-per-day pass for a park that closes early.
