I'm looking at the back of a coupon right now (single-day pass to club acela or 10% amtrak discount). There are a couple of bullets, but nothing that seems to indicate that these can only be used by a Select or Select+ member.

There is one that says that "Other restrictions may apply." Pretty generic, but like the_traveler says, Club Acelas are only in those 4 east coast stations.

If you're trying to use one in Chicago...good luck ^