I just went to Disneyland, in February. Alas, the Electric Shocker is there, but it’s retrofitted to just vibrate, now. 
Let’s see, though…off the beaten path?
•It’s down to only a few machines, now, but they’ve still got a few Mutoscopes running in the Penny Arcade. Price: 1¢.
•To be found, and visited in Adventureland: Shrunken Ned, and Raja’s mint.
•The actual walk-through diorama inside Sleeping Beauty’s Castle is open, again, and newly refurbished—some of the effects used, I actually couldn’t figure out how they were accomplished.
•The (virgin) Mint Julep bar in New Orleans Square.
•If you have a smartphone with Shazaam (or a comparable app), you can actually have it identify the sometimes obscure non-Disney ambient music playing in various areas. I found some neat Cajun music that way.
•Go on a self-directed Disneyland Death Tour!
•…or a Disneyland Ghost Tour!
•Spot the skeletons in Pirates of the Caribbean—the remaining real ones!
•The Magic Shop on Main Street is still up and running, and a fun little visit…they’ve got some handcuffs used by Houdini behind a display case.
•Although it’s not running at the moment, you can still walk about the Mark Twain, and a display board near the entrance has some photos of notable historical figures who’ve visited, over the years. Some of which aren’t available online.
•Check out the pet cemetery.
•Visit the Heraldry Shoppe in Fantasyland. Buy framed family Coats of Arms, emblazoned shields, or just some swords, axes, and knives! Actual, metal, bladed ones!
And I know you said you don’t plan on doing any park hopping, but I actually would recommend the California Adventure—I admit, I’d always been skeptical about the whole idea, but upon visiting (especially helped by the remodel they’d done, a few years back), it was really beautifully executed. And I found the atmosphere actually quite relaxing, compared to the exhilarating-but-exhausting Disneyland proper.
But, more to the point, I thought many of the CA shops did a bit of a better job of presenting more unique, theme-specific merchendise—the Off the Page shop, with a lot of animation related books, comics, custom artwork, etc, and Humphrey’s Service and Supplies, which carries more outdoorsy stuff—including actual redwood seedlings. The Tower of Terror shop has some appropriately unnerving merch.