The poster used the wi-fi in the Pacific Parlour Car, a special lounge car which is reserved for Coast Starlight sleeper pax (except during the daily wine tasting hour, for which the crew sell extra tickets to coach pax). It at least seems apparent that the poster was going sleeper and that the service manager implied that a $5 wi-fi fee would apply to everyone.

Also, the value depends on how much access each $5 session would buy. 24 hours wouldn't come close to cutting it if you're going the full length of the Coast Starlight, or most long-distance routes.