You should rest assured that draftsight would help you move to 3D in a relatively easier manner. The software would enable you to preserve the overall value of your 2D DWG data providing the best available tools. You should rest assured that these tools would be able to convert data from 2D to 3D in the best manner possible.
They would also be used for accommodating reusable 2D geometry. They would also enable you with a relatively smooth transition. It would be pertinent to mention here that the transition would be inclusive of extensive assistance documentation for all AutoCad users.