I think you have to jump all the way to fully protected bike lanes to get a widespread shift going.

A very small improvement in the width of the unprotected bike lanes would not be enough for the majority of potential bike riders. Then, the opponents have the opportunity to point out the lack of use and crow that the whole idea is a waste of time and money.

But a big change would have a big response, and would relieve a lot of commuters from their reliance on cars. Then the argument that bike lanes are worth the cost and space in cities would have some results to back it up.