OK...so how about comparing the value of an Amtrak mile vs. an airline miles, such as UA?
I have about 40,000 Amtrak miles from BOS-NYC Acela trips...maybe I should transfer 25,000 this year and the balance next year to UA or CO vs. leaving them in Amtrak?
By the end of next year, I'll probably have 50,000 Amtrak miles...