Hell no!
I would love to know how many commuters actually use AMTRAK a year. There is no justification to extend commuter rail in Milwaukee.
Everytime this is brought up it reminds of a Simpson's episode when they build the Monorail.
How about we just give the commuters from Milwaukee to Chicago skateboards. Now there's an idea I support.
The Wisconsin DOT (PDF document) does list how many people ride the Hiawatha last year, and that was 397,518 passengers. That's for 6 daily round-trip runs and 1 additional Monday-Saturday round trip run.
To do the math, first divide that 397,518 in half to 198,754 actual riders (roughly, there are probably a few that don't make the round trip). Then divide by 52 weeks to get 3,822 riders per week. Divide again by 48 round trips per week to get just under 80 riders per round trip.