Without knowing any more details about the 2 options you have (cash or points) I can give you a quick summary about what makes Amtrak unique among point programs.

1k Trips - These special routes may cost $50 a trip so spending the miles is prob. the best use in the program.

Sleepers - These are a large number of points but fit 2-4 people into an award which makes it an excellent value. This is only for people who take LD trains with sleepers. It's a great redemption for people who would take this type of train (as opposed to commuter type lines which is what is mainly found in the NEC which handles most of Amtrak traffic).

NEC - For 3k you can redeem trips from Montreal - New York, New York - Washington and almost all points between the 2 cities. In peak times these tickets are $100+ which makes the 3k a great value.

Also tickets are refundable as long as you don't print them out from the quik ticket machine (if you have printed it already then you need to mail the actual ticket to Amtrak which takes time).

Few blackout dates and no capacity controls means you can book the emergency ticket with no hassle and no extra miles. There are no fuel surcharges or even tax.

If any of my information is incorrect please correct me and feel free to add anything.

Back to the OP, the value of the points depend on if/what you want to use the points on, and the particular route you are taking. Most people take the same few routes and learn the ticket prices to arrive at their valuation. I would say .02 would be the lowest valuation for an Amtrak point. Use cash for any valuation under that.