Agree with wxguy.

Don't choose Amtrak for S+. S+ really does not measure up relative to airline programs. You get almost zero preferential treatment, just a few coupons and access to Club Acela which is not worth all that much.

But, despite that and all the endless CS problems I've had (some documented here) Amtrak does have its upside:

1) Its locations are usually more convenient than airport.
2) You don't have to go thru the hassles of going thru security and can literally get to station 2 mins before departure
3) It's more reliable and predictable in bad weather than shuttle
4) Almost everything is refundable, cancellable,