In the '90s when I was active in parallel computing (compilers, algorithms, architectures) I had the perception that the number of parallel computing publications was multiplying to fill the market, and the growth had little to do with the number of quality papers produced in the field. Maybe this was necessary for the increasing numbers of researchers seeking tenure, but I think it hurt the quality of research in the field.
It was hard to tell which tail was wagging what, but researchers "needed" more publication venues, and libraries and researchers "needed" to subscribe to more journals.
August 5 NPR's Science Friday, there was a pair of guests talking about retractions in science journals. An interesting comment one of them made was that with more publication venues, especially with the growth of online publications, the number of items to be reviewed is growing faster than the number of reviewers. This must impact quality in a negative fashion.