Other then being "surrounded" by the magic. There is no real benefit (IMO) to staying on property VS one of the Hotels accross the street on Harbor Blvd.
Transportation is a non-issue with
Disneyland, as everything on property is within walking distance. You walk between the parks and to DTD. The parks are connected to the Disneyland and Paradise Peir Hotels via Downtown Disney. Other then "priority" on the Monorail from Tomorrowland to DTD, there is no transportation benefit.
Early Entry. This is something that is just starting to be brought back to Disneyland and is only at the Disneyland Park (DCA is not included). I am also not sure if this is included with any Disney Hotel stay or just for those who booked with Disney Travel Co. In the past it has included all hotel guest, those who purchased Passes through
AAA and those who purchased packages throught DTC. Right now, from what the limited information that I have read, it is only those who book through DTC.
Now the Grand Californian is a great resort/hotel. If cost were not a factor that is deffiently where we would stay, hands down. But with rooms costing close to $300 a night, it is just out of reach. Discounts are not available like they are for WDW. You can get a good room rate at Paradise Peir and sometimes at the Disneyland Hotel. But for my vacation money I would prefer to save on accomidations and spend it in the parks on treats and souvenirs.
Now at WDW on site is the only way to go, I agree. The same is not true at Disneyland.