What does Auto Orientate do in the Vector Import dialogue for SketchUp?
As most components want to be cut so that the largest face is face up on the CNC Router, if this option is selected, all the components in your Sketchup file will be rotated so that the face facing up is the largest.
If your design requires thin pieces that have a thicker profile then face, this option may not be suitable. Position your components within Sketchup with the correct orientation for cutting before importing.
If you are finding that your top face is not being used as the top face by the Sketchup Importer, (due to having a smaller surface area then the bottom face) then you can force it to stay the right way up by adding a colour to the top face in Sketchup.
Then when you are importing the vectors into Aspire/VCarve you can change the Orientation option to "Orientate by Material" and pick your colour from the dropdown menu. This will inform the importer exactly which way up you need the model be.