Features conflicts when field bases are used by other feature
Say you have two Features, and one field that is used in both Features, then you only need to export the field base ONCE.

This is why I generally have a "controller" Feature that contains field bases, update hooks etc, and then for every other Feature I export the field instance, and then add a dependency on my controller feature.

Basically, you are right - you don't need to export the field bases every time, just export them once and then add dependencies.