Throw it away - as you've mentioned its bind on account and cannot be sold on the auction house.
The plans for the later difficulties are not farmed, they're purchased from a vendor in Act 4 so to get the recipe for the Nightmarish Staff you need to do the following:
- Start a Nightmare game on Act 4 Quest 4 Part 2 (The Prime Evil - Enter the Crystal Arch)
- Go to Gorell the Quartermaster, near the healer and the followers.
- Buy the Plans: Nightmarish Staff of Herding.
- Go to the Blacksmith and use the plans.
- Craft the Nightmarish Staff of Herding by having 200,000 gold and the Staff of Herding in your inventory.
It is worth noting that the chance that Gorell has the recipe is not 100% - if he doesn't have it in your game simply leave the game and re-create it until he does. You will need to do this for each difficulty, so nightmare for the nightmarish plans, hell for the hellish plans, etc.
Hope it helps