It's new equipment that will deliver the most bang for the buck.
If one Billion was allocated for new cars that would probably add 300 revenue cars and the rest non revenue. That would increase yearly ridership by at least 10M. $1B spread of 4 new routes would not increase ridership that much ? 4 new routes would need what in cars ? 16 train sets? = 80 new cars to finance ? $249M ?
Maybe someone else can speak to the cost of a mini-order of 80 new cars. I want to see new cars ordered by the 100s.
Could 4 new routes increase ridership by at least 10 million? No way. Not with $1 [edited to match previous comment] Billion to start new trains.
Extending the City of New Orleans along the Gulf Coast is predicted to get 140,000 new riders, iirc. No telling what it will cost to make a deal with CSX. If we're lucky it will be the PTC and signaling and not much else.
More easy pickings: Take the Cardinal daily. Probably CSX will make it costly to do. But daily service would almost double the 3/7th train that carries 105,000 riders now.
The sad sack Hoosier State could find a purpose in life if it ran daily to complement the Cardinal's service. An Indiana State Highway Dept study a couple of years ago suggested that for $250 million the route could be made 29 minutes faster, with track upgrades in Indiana alone (ignoring potential time savings from pending CREATE projects in Chicagoland). Then a Hoosier State running with owning departures from Chicago AND Indianapolis could have ridership in the 80,000 range, instead of the measly 30,000 it got last year.
Taking the Sunset Ltd daily west of San Antonio would again double ridership, according to the PRIIA study, so pick up a quick 100,000 new riders thru the desert.
The 2009 study concluded that the Sacajawea (a.k.a. the North Coast Hiawatha) could add a net 360,000 new riders at that time. It's performance, 58.0% firebox recovery, rivaled the best long distance train in the stable, the Empire Builder with 65.7% firebox recovery, and in 2009 51.8% for the LD trains as a group. (Updating a bit, last year FY 2016, the Builder carried 455,000 pax.)
Well, I may have spent your Billion before I even got into Montana and North Dakota with the Sacajawea. Keep in mind that the host railroad always finds problems in need of costly fixes. Opening or reopening stations, training new crews, etc. -- that stuff adds up.
For roughly $10+ Billion the Stimulus is getting us greatly improved routes Seattle-Portland, St Louis-Chicago, Dearborn-Ann Arbor-Kalamazoo-Chicago, Charlotte-Raleigh, NYC-Albany-Schenectady, and New Haven-Hartford-Springfield. It's all good, and I'm an optimist about there being a huge untapped demand for trains. But for the $10+ Billion from the Stimulus, I'm looking to see only about 500,000 more riders in FY 2018, maybe cracking a million more on board a few years out.