You can transfer CO miles to Amtrak Guest Rewards points at 1:1. 15K miles will get you a one way, one zone trip in a roomette sleeper, 20K in a bedroom sleeper, with one travel companion for free and free meals along the way. No full body scanners either
If you live in Boston, Acela trips are also an option.
However, Amtrak is a poor holding tank. Transferrring out to another program takes $200 on paid travel charged to the AGR credit card in a year, or Select status, I believe.