I routinely go to a conference at the Anaheim Convention center,stay at Anaheim Hilton, and I go to
Disneyland in the evenings. I take the ART, which costs about $20 for a 5 day ticket. It's $20 per adult, of course. I don't bring a car with me. I take Supershuttle from the airport (which costs about $11 each way). The ART bus comes about every 20 minutes, and there are at least 3 routes that stop at the plaza between the Marriott and the Hilton. It also seems like it would be a reasonable walk. One year, my husband and son came and we rented a car. I got a bit aggravated with my husband because he wanted to drive and not take the bus. We walked further and waited longer and paid more than we would have with the ART bus.
Unlike at WDW, however, there are not free shuttles to the parks from the hotels.