I read somewhere that Salinas is to Monterey as Oakland is to San Francisco; overlooked, less developed, cheaper, and with a bit of a chip on its shoulder. Of course, Salinas doesn't have a waterfront, which is a serious problem from a tourism point of view. However, it does have just as solid a claim to Steinbeck as Monterey.
I don't know much about the history of the creation of the National Steinbeck Center, but I can assure you that it is one of if not the best literary museum in the United States. Tourist guides say so, so it must be true. No, in all seriousness, it is an impressive museum, with tons of interactive exhibits for the kids (you can pick a pony's hoof in the Red Pony section, which actually is a little macabre -- I mean, it's a hoof. A real hoof. No longer attached to a pony). Tons of screens constantly show clips from Steinbeck films and plays. Quotes are everywhere, some manuscripts are on display, recreations of settings and so forth. The single best exhibit is Rocinante, the custom-built truck/camper/Winnebago that Steinbeck drove around the country on his Travels with Charley, the most famous and well-regarded of his late works. My photo of it did not come out too well, sadly.
Just a couple of blocks away from the museum is Steinbeck's childhood home, mentioned in East of Eden. It's now a restaurant, which sadly was closed on Memorial Day. Oh well. Authors' houses are sometimes barely interesting when they're set up as museums, let alone as restaurants. I'm a trifle surprised that there was no move to make this part of the museum; I don't know if there's any real relationship between the two. We also drove past the high school, but I skipped the graveyard where his ashes are interred. Some were scattered into the wind on a seaside cliff in California, a fitting memorial.