When unsetting a VAO, should you also unbind the associated VBOs?
No, you do not need to unbind the VBO's. VBO's are only added to the state of the VAO when that VAO is bound. So any previously bound VBO's will not alter the state of the VAO that you are going to bind. The state of a bound VAO can be changed with the following calls:

glEnableVertexAttribArray
glDisableVertexAttribArray
glVertexAttribPointer
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER)

You can bind and unbind VBO's without a currently bound VAO and even share them amongst VAO's. The VBO is simply a pointer to a data container that can be used for multiple purposes.