Here's the report that generated the news
over the past couple of days. I'm still digging into it.
1997 was a low point for Amtrak, so it may be disingenuous to start there, though it was also the year when a major piece of reform legislation passed. Here's a graph I made for system-wide ridership from Amtrak's inception through 2010 (I should post an update at some point -- they reached 31 million last year):
Amtrak ridership 1972 to 2010
, on Flickr
I don't think the Empire Builder has seen ridership go up as quickly as the system as a whole, but the frequency of service has remained daily. I'm pretty sure we have the busiest stop for a station that only sees one train per direction per day. The only exceptions I've found are the endpoints of the Auto Train, which runs non-stop between the D.C. suburbs and Florida (poke at long-distance train numbers for a while, and the Auto Train tends to be the exception for many measures).
I made this map last month showing ridership at stations all across the Amtrak system:
, on Flickr
A point I've been trying to make with the map is that ridership is pretty closely tied to frequency of service all across the country. It doesn't look like a standard population density map at all -- The Empire Builder actually looks very good in comparison to the other western routes (the once-daily California Zephyr and Southwest Chief, and the thrice-weekly Sunset Limited along the southern border). That's more or less backward from what you'd expect, especially since there aren't any major metropolitan areas between the Twin Cities and the west coast along the Empire Builder route, while (for instance) the California Zephyr hits both Denver and Salt Lake City.
I imagine the only way we'd see ridership increase from Saint Paul more than another 20% or so would be if more trains run. We could certainly do better with the current train if it could arrive and depart on time more consistently (particularly eastbound), though taking a thorough look at the route to see if any connecting bus routes could be added, advertised, and/or integrated into the Amtrak ticketing system would also be a good idea. Amtrak suggested that they'll add a bus route between Grand Forks and Winnipeg soon, but I'm not sure if that's actually progressing or not. Some bus routes have been added in Wisconsin in recent years, though I don't know how popular they are. (I still haven't taken an intercity bus in the U.S. -- the idea of being dropped off in a McDonald's parking lot next to the highway doesn't really appeal to me. If buses are to be taken seriously, they need decent infrastructure too.)