What do paywalls possible have to do with the reproducibility of results? Anyone who has access to a lab capable of even attempting to reproduce such research is either 1) at an institution that has access to those journals or 2) can use google to find the papers anyway. Hopefully both.
The fact that tax-payer funded research is put behind paywalls is a travesty , but it seems wrong to claim it actually hinders researchers from doing anything given.
Even if they are closed, you can link to the papers (unless the DMCA metastasized again). Granted, someone can't make an automatic tool to find such studies, but that would be hard anyway and presumably the authors are aware of the study they are refuting and could tag them.
Now, people trying to make policy decisions could not read or evaluate the studies. If we assume they are capable of doing so in the first place( i.e. their not Lamar smith), then we have an actual argument for getting rid of paywalls. I still think the best one is its a waste of money and a tax on universities/ grants.