Best Practices

Yes we should do selective upgrades only. Bear in mind that not specifying a version won't prevent you from updating selectively the gems you want.

The biggest problems we had with fixing versions in the Gemfile is that you will keep having the same versions of the gems that were there when the project started, when probably those gems got security fixes, performance improvements etc... We used to have a capybara version realeased 2 years ago that brought bugs to our acceptance test suite.

Not specifying versions promotes the behavior of updating often.