We are Disneyworld vets, but have been to Disneyland in July for the last 4 years, and in June for a few years before that. If we had one day, we would absolutely hop. Hopping is nothing like WDW. It is a 5 minute process. You do not even go through security again to hop between parks. The parks are separated by a Plaza the size of a football field. WE literally have gone from the very back corner of DL to the very back corner of CA in 10 minutes. You don't want to miss at least seeing Carsland- it is amazing and we aren't even Cars the movie fans. Assuming everyone is old enough, you can single rider Radiator Springs Racers without too long of a wait, so if you were to hop over after Fast passes were gone you can easily do that. RSR is one of our absolute favorite rides in any of the U.S. Disney parks. You will never see Test Track the same way again. The Guardians of the Galaxy redo on TOT is really fun, if you like Guardians. Although I liked the look and theming of TOT, I was never a fan of the ride itself- and now I almost (LOL) enjoy it.
The nice thing about DLR, is you don't have to have a firm plan. You need to know what the most popular things are that you want to try, and you need to figure out the timing of those, but other than that, it has wonderful flexibility. The only thing we miss from WDW when we are at DLR is EPCOT, and particularly World Showcase. You can definitely hit all the main highlights from both parks- DH and I have done both parks in a day on a business trip once and ridden almost every ride in both parks, but it does require a fast pace! Two days would definitely be better- if you can swing it (we typically like 4 or 5- but would take whatever we could get). Evening entertainment will be difficult for one day- you will probably have to make a choice between Fantasmic and World of Color. I would say World of Color as it will be entirely different from anything you have seen at WDW, and if you can swing it and they still have it, I would recommend the dessert party. That way you get a chair. You get to wait for the show to start in a chair while having food and drink and you aren't forced to stand during the whole show, and if you are short like me, to risk seeing someone's back instead of the show.
If you can do the 2 days, that would be even better, but we would still do hoppers. I would feel constrained not to have hoppers at DLR. We have been known to go back and forth several times a day. Also, if one park is starting to feel really crowded, we look at the wait times and if they are shorter in the other park, we hop over. That can be pretty helpful in the summer months. I remember one July day last summer when we hopped to CA because the lines were getting long at DL, and the line for GOTG was only 45 minutes (which being new- that line was known to be 2 hours a lot of days), and RSR only 20 minutes. This was around noon, so not early in the morning. It was a great hopping day- we went back to DL later.
You don't need to worry about the EMH park at DLR like you do WDW, it will not make it significantly more crowded for the full day. They have a much bigger local crowd. The lines will be slightly longer if you get there at EMH end, but the first two hours of regular opening are typically still great. With the local crowd, a lot of people just don't get there that early.
DL, used to open an hour or two before CA, but since Carsland opened, they mostly open at the same time, which is usually 8:00 a.m. in the summer. CA closes before DL. In the summer, CA usually closes at 10:00 and DL usually closes at midnight. We often hop from CA over to DL when it closes (or usually if we are not at WOC that night we try to get out of the park before the rush after WOC to hop from one park to the other-- which still doesn't take that long- but typically there are no lines if you beat the rush).
