I tend to assume OSS contributors/maintainers are working generally to make things better, features I'm not using/don't need aside, they're fixing bugs (that I might not know I'm hitting/about to hit), patching security holes, etc. - so that's one for the 'pro-upgrading' column.

Against that, sure, there might be something bad in the new release (maliciousness aside even, there might be a new bug!). But.. there might be in the old one I've pinned to as well? Assuming I'm not vetting everything (because how many places are, honestly) I have no reason to distrust the new version any more than my current one.

Reproducible builds are an orthogonal issue? You can still keep your dependencies' versions updated with fully reproducible builds. Ours aren't, but we do pin to specific versions (requirements.txt & yarn.lock), and keep the former up to date with pyup (creates and tests a branch with the latest version) and up to date within semver minor versions just with yarn update (committed automatically since in theory it should be safe, had to revert only occasionally).