I did the Marathon as part of the Inaugural Dopey Challenge in 2014, and really enjoyed myself. Not planning to do it again until 2018 (Dopey's 5th anniversary) though.
I stayed at Disney's Pop Century Resort, which is one of their value resorts, but all in all a nice place. And I did like the couple of training runs I did around Hourglass Lake in the morning.
I do feel staying on property was worth the extra for the event transport. Jumping on a bus in the morning to get to the start, and then on another one when you are ready to come back to the hotel took away a lot of hassle.
I must add that I was solo though. If you are going with others then obviously you will have a lot more things to consider.
I've never run there, but I have been to Anaheim twice for the Convention Centre, which is just down the road.
There are LOADS of hotels around there, with every price range accounted for. There are Disneys own properties that are on the expensive side, to the cheaper "no frills" type of place.
I personally haven't decided yet where I'm staying. I've used the Hilton on the 2 times I went before, but they are a bit pricey, with little in the way of extras. I am currently looking at 2 places. The Anahiem Fairfield Inn, which is very near the front gate of Disneyland, and the Clarion which is probably about half a mile away, but a LOT cheaper.
As for things to see and do, other than Disneyland. Most things are a fair drive away, but easily doable in a day. I've personally been to Griffifths observatory, Hollywood Boulevard, saw the "Hollywood" sign, and last time my friend and I went to long beach to see the Queen Mary, we were going to go to Universal Studios Hollywood, but didn't have time in the end. Expect to pay for hotel car parking though, I have yet to find a hotel that doesn't charge, and so tend to just rent a car for a day or two, you don't need one for Disneyland unless you do stay a long way out.
Well, I've just signed up for Dumbo. If I'm going to do this, I might as well go all in and go for the Coast to Coast.
Admittedly that was the plan from the start, but you never know how things will turn out, after all the Dumbo sold out in something like 6 hours last year.
No 5k photos here either, so I may just have to get the other three races, as the "deadline" is the end of the week. Not that I particularly like the pictures of me (never feel too photogenic), but there are a couple I do like and for the price you may aswell buy the lot.