Dave,
I agree -at the moment there are not enough extra features in inf compared to complete to justify the extra money. However, things may change in the near or farther future.  I am not sure if it is of general interest but these are the feature I might want:

-Control procedural terrain altitudes based on relationships with other objects   
-The altitude of procedural terrains can be dynamically affected by other objects    
-User definable geometry anti-aliasing    Up to 1024 rays/pixel   (well, more than 64)
-Control materials based on the properties of other objects
-Animation features
-Change interface colors/size of text (so I can see easier)
-Ability to reorganize the view panes
-Python scripting
-Python console for direct input of Python commands
-Python functions to add, modify and remove EcoSystem instances
-Macro recording and playback to automate repetitive tasks

Some of these I would use right now(eg interface color), some I would use when I get more proficient (the procedural terrain and material control features), some I may want to use if I work a lot more with vue and need more efficiency (python, macro recording)

It is more a question of having options in the future than fixing something right now. Even if they claim inf is for pro's maybe I/others would like to turn pro? 
Also worrying, as was mentioned already, what will happen when v8 arrives ? will the gap in features grow? will it be possible to change tracks then?

( I would also like to know when skinvue for v7 complete?)

"I paint that which comes from the imagination or from dreams, or from an unconscious drive. I photograph the things that I do not wish to paint, the things which already have an existence."
Man Ray, modernist painter
http://artpearl.redbubble.com/