Since you're staying at the GC...for a really nice dinner I recommend Napa Rose! Steakhouse 55 and Hook's Pointe over at the
Disneyland Hotel are good, too. If you want to eat in the parks...lots of people really like the Blue Bayou, but I'm not much of a fan - the atmosphere is great, especially if you get a table next to the water, but the food is mediocre for the price. I like the Vineyard Room at Disney's California Adventure, though for a more moderately priced meal, the Trattoria is good, too. You can find menus for restaurants at the Disneyland Resort at:
http://allearsnet.com/dlr/din/menu/menus.htm
Driving Directions...From John Wayne, I would take the 55 freeway to Interstate 5 north, then get off on Harbor Blvd. At the light at the top of the off-ramp, turn right, then get in the left lane and turn left at the first light onto Ball Rd. At the second stop light, turn left onto Disneyland Dr., then stay to the right - following the signs to Downtown Disney/Resort Hotels rather than to the Theme Parks. I believe that the left turn into the Grand Californian is at the second stop light - it's marked, though. You can pull into the entrance and have your car valet parked, or if you want to self-park, you can leave your car while you check in and get your parking pass, then take your car to the parking lot across the street.
Since you're familiar with WDW I would suggest doing things that are unique to Disneyland/DCA, or substantially different, like a lot of attractions in Fantasyland, Roger Rabbit's Cartoon Spin, the Indiana Jones attraction, Disneyland: The First 50 Magical Years, the Matterhorn, Space Mountain, Pirates of the Caribbean, the Disneyland Railroad between Tomorrowland and Main Street, and Pirate's Lair on Tom Sawyer Island. At DCA, don't miss the Aladdin show - it's spectacular. California Screamin' is a great coaster, and Monsters, Inc. is fun. The Animation Building has some interesting things to do, though I guess a lot of the interactive activities there are at Disney-MGM Studios now.
In late October you'll be there for the Disney's HalloweenTime celebration - lots of decorations and special things for that! The parks really look great. You'll also be able to see Haunted Mansion Holiday, which I think is really well done.
As a resort guest you'll be able to do Early Entry at Disneyland on the Monday and Tuesday of your stay - DL opens an hour early. Most of Fantasyland and several attractions in Tomorrowland (including Finding Nemo Submarine Voyage) are open during EE.
Depending on your October dates you might also be able to attend one of the Mickey's Halloween Treat parties at DCA - they aren't as elaborate as the Mickey's Not so Scary Halloween parties at WDW (no special fireworks or parades), but there's lots of trick-or-treat stops and special lighting and decorations, and it's a fun event. There's more information on it at
http://allearsnet.com/dlr/tp/dca/mht.htm
Hope that helps!