I was born in L.A. but moved so often that I've been to DL and WDW an equal number of times. Just like I wouldn't recommend going to Orlando and only visiting MK, I wouldn't recommend going to Anaheim and only visiting Disneyland. If you're only going one day, I would do both. Yes, a lot of the rides at DL are similar to those at WDW, but there are some differences even within the same rides.
I LOVE DL and prefer that park by far, but DCA has its place as well. If you've never been, you should at least park hop so you can experience a little of both parks. My favorites at DCA are the Frozen show (it's AMAZING), Radiator Springs Racers, and oddly enough, Mater's Junkyard Jamboree, haha.