An advisory committee is a totally different beast from data derived from customer surveys. In my professional career I was a member of the Scientific and Technical Advisory Committee (STAC) for the Chesapeake Bay Program, and I was also a staff manager ("Designated Federal Officer") for a couple of advisory committees run by EPA. The EPA committees were managed under the terms of the
Federal Advisory Committee Act (FACA), which requires stuff like balanced membership, advance publicity for meetings, including advance copies for the agenda, all meetings open to the public, the committee publishes its recommendations, and (usually) the Agency makes a response. The Agency getting the advice can ignore it all they want, but the committee's advice is in the public record. The Chesapeake Bay STAC was actually fairly successful getting positive responses to technical issues they raised. The members serve as "volunteers" (though their employers usually cover their salary while they do committee work). For the EPA Science Advisory Board, we would pay a nominal consulting fee to certain academics and representatives of NGOs to ensure their participation, especially if their organizations couldn't afford to cover salary.
If Amtrak were to have real outside advisory committees, they might not have to follow FACA rules fully, as they aren't a true Federal agency. (On the other hand, if DOT had an Amtrak advisory committee, with would be entirely under FACA and would be officially giving advice to DOT, not to Amtrak.) While Amtrak itself would need to manage the committee, it would be perfectly proper (and useful) to have members representing RPA, AAR, individual host railroads, states that support Amtrak service, commuter agencies, the unions, etc. I could see two committees, one that focuses on passenger services and policies, the other that would focus on operations. Even if Amtrak ignores the advice, it would disseminate responsible discourse about the issues from reputable stakeholders. And I don't think Amtrak could totally blow off a recommendations submitted to the public record by a committee composed of its main stakeholders.