Update: If you start to book a fare on Amtrak.com, when you get to the payment page, there is a better offer: 40,000 bonus points PLUS $100 statement credit. You don’t need to go through with the booking. H/T to DoC. For a limited time, Amtrak is offering 40,000 Guest Rewards points as a signup for its World Mastercard. This is double the usual 20,000 points, though the spending requirement is $2,500 (instead of $1,000) in the first 3 months. It’s a great deal for those who travel using Amtrak. Each Guest Rewards point is generally worth 2 to 2.5 cents. That makes the increased signup bonus worth around $800 to $1,000…