The managed lane on the Eisenhower will very much NOT pay for itself according to projections. One lane doesn't bring in much revenue unless you raise the prices to astronomical levels (which just invite
political blowback). I think it's still a good policy regardless.
The tolls won't make a dent in the full Eisenhower project which is a total rebuild of everything through a densely built-up area. However, a similar project on I-55 might pay for itself because IDOT already future-proofed for a 4th lane back in the early 2000s. There were discussions under Rauner to bring in a private operator to build/operate those I-55 lanes but that conversation died off awhile back.