The short answer is that versions prior to version 6 were the best ever written for purposes of vector digitizing and editing. They are easier and more powerful, definitely more intuitive, and, for my old eyes, very much easier to see what you are doing.
Some of the features lost as the product has evolved:
1. The ability to make a bitmap into a guide. The old version moves an image to a different layer and it is totally unselectable until you want it to be. The newer versions, disappear when made into a guide so you can only lock them on the same layer where they are still selectable. When zoomed in, the bitmap will often become selected unintentionally which interferes with editing.
2. The display of a vector made into a guide is a gray continuous line in pre version 6 making it very easy to clean up autotraces. Just duplicate the trace in place and make it a guide. Post version 6 displays guides as dotted blue lines and lack the display accuracy of the older way. Both post and pre version 6 have great path cleanup tools. The difference is being able to see the original adequately to remain faithful to it.
3. Pre version 6 uses a logic of locking the position and angle of control handles on nodes, allowing only the length to be changed when dragging a path segment. Current versions use the "rubber band" approach which moves adjacent segments as the angle of the control handles is allowed to be changed when dragging a segment. I find this totally annoying.
4. Pre version 6 allows for snapping the angle of a control point handle to 90 degrees or zero degrees by depressing the shift key. Post version 6 does not.
5. Pre version 6 provides an ingenious tool set which provided for easy capturing of the length and/or angle of any line segment and then applying either to a different line segment. This now missing capability made it possible for anyone with a basic understanding of plane geometry to quickly edit objects into perfect geometric shapes. Things like truly parallel lines, equilateral triangles, ovals and ellipses are a piece of cake.
6. Pre version 6 has a routine called a "3 point circle". Simply click on three positions where you want a circle to be and a circle is drawn that will most closely go through the three points supplied. Newer versions have routines with similar names, "2 point circle" and "3 point circle" but neither works anywhere near as well.
7. Pre version 6 had the ability to keep or delete a path when outlining or inlining. Very useful choice to have. Post version 6 lost this option until after a lot of requests from yours truly, it has finally been returned in the current version 7.6v2.
8. Pre version 6 has better visibility of nodes and control handles when vector editing on top of a bitmap image being used as a template.
You really would have to use each for a while to see how vastly superior the old version is in so many ways. In fairness I would point out that post version 6 has got lots of neat things added ... not the least of which is 32 bit code. Pre version 6 is a 16 bit application and will not successfully run on Windows XP.