I have tried to pressure Kayak, Sidestep (now owned by Kayak), and some of the online travel agencies like Travelocity, etc., to include Amtrak routings in their ticket search results. Travel agencies can sell Amtrak tickets, I believe, so Amtrak city pairs and fares are published to GDS systems. Therefore, it shouldn't be too difficult for some of these sites to add Amtrak to their results.
I believe that if Amtrak travel were more visible to the general public, people might be more likely to book it--especially if the fare is less! (Most of our population probably doesn't even know Amtrak exists!)
I've also written Amtrak and asked them to share their data with
Google Transit--I imagine a day where I can search for directions from the Queen Mary in Long Beach to the Smithsonian Air and Space Museum in DC and receive a seamless set of directions across multiple transit systems from start to finish!
I think both of these options would help increase train travel immensely...