Another arugment for the money spent is that it would take truck traffic off the highways. The problem with that is that products arrive from China or where ever and are then railed to the Chicago area distribution points. I believe these distribution points are in Bedford Park and somewhere around Rockford. From there trucks pick them up and deliver them downstate. The quantities being delivered downstate are small enough that it would not be cost effective to ship them by train. Additionally, when products are delivered downstate it is to small towns which do not have rail service. Take a look at the map of Illinois. Once you are out of the Chicago area there are mostly small towns. I don't see rail service coming to these small towns any time in the future. Trucks are here to stay.
You're just thinking locally though. Probably half to 2/3rds of all freight trains pass through Chicago. So while the small local town may not see an immediate benefit by improving this line, freight can now get to Chicago and those distribution points that you mentioned much faster and easier. And remember that Union Pacific moves large amounts of freight out of Los Angeles Port on its Sunset route to San Antonio. Those freights would then come up the line in question to Chicago where they might head to a distribution point for dispersal to the small towns.
The better & faster freight moves, the cheaper it is for the consumer. And the more freight that can be moved by train, the less impact on our roads and the less subsidies that our roads will need.
I remain firmly convinced that this is a good thing for everyone, including those in Illinois paying the bills. This line will help to prove to the many naysayers that one doesn't need the likes of Boston, NY City, Philly, and DC to have higher speed trains.
Additionally this will lead to further funding for this line, so as to increase the speeds on the northern end to benefit still more people.
Finally, please let me leave you with two other thoughts. One, this will see improvements made to some of the Illinois stations, which will benefit the locals. Two, part of the money being spent here is being spent on new cars. That alone is a huge benefit for the locals, having brand new modern cars.