Is there any great reason to stay on property? (I was shocked to see the price tag for PPH was more than I'm used to paying at WDW.)
Any reason to book a Good Neighbor hotel through Disney instead of Priceline/Expedia?
There is less benefit to staying on-site at DLR as compared to WDW. Yes, the DLR hotels are within walking distance of the parks, but so are several off-site hotels just across the street on Harbor Blvd. (in fact, some of them are faster walks to the front gates than the Disneyland Hotel). The one major benefit is EMH, which is better at DLR than at WDW. You can get a lot done in that first hour. But, is it worth the hundreds more that you will spend on the on-site hotel? I personally don't think so.
1. If we only do one day at Disneyland, and we're there before rope drop and intend to stay until closing, can we afford to leave the park for lunch? (As long as we can get on Rise of the Resistance, meander through SWGE a bit, and squeeze in a few class attractions, the rest is gravy.)
I think you could afford to leave the parks for lunch, as long as you're just having lunch in Downtown Disney. I would avoid having to walk further or drive away for lunch, with you having only one day. I also just don't think it's necessary, as DLR has many great food options, especially quick service.
2. What're the best quick service restaurants in the park? (We eat everything, but usually go for the most unusual option - unless there's bbq. Then we'll always get bbq. Unless it's bad bbq. Then forget that bbq. But sometimes... even that bbq.)
I'm sure you'll find many useful threads on this topic. Most people who've been to both DLR and WDW tend to say that WDW has better table service options, but DLR has better quick service. This has been my experience as well. I rarely make dining reservations at DLR, because there's so many quick service options that I love going back to. I am fond of the gumbo bread bowls at the Royal Street Veranda. Fried chicken at the Plaza Inn is excellent. Bengal BBQ has some good skewers (I do think they're a bit overpriced for the small amount of food you get, but I still splurge every now and then as a snack). The new Tropical Hideaway has some yummy options too.
3. Finding Nemo Subs and Matterhorn - worth the time in a 1-day touring plan? (I love classic dark rides and my husband is all about big, big thrills.)
I definitely think it's worth doing Matterhorn. It can be a bit of a bumpy ride, but it's still worth it. Try to ride at night if you can - the surrounding lights during the portions where you come out of the mountain are quite lovely. I would personally skip Nemo. It's usually a long wait, and a long ride. I've only bothered to do it once in my last four visits, even though I had time to ride if I had wanted to.
The rides I consider must-dos for every trip: Space Mountain (the DLR version is smooth as butter and better than WDW's version, I love it), Indiana Jones, Big Thunder Mountain Railroad, Matterhorn, Peter Pan, Pirates of the Caribbean (again, superior to WDW version), Haunted Mansion, Disneyland Railroad, Story Book Land Canal Boats (so cute and unique, and one of Walt's favorites).