There are 875 individual aircraft folders, inside the FS9/Aircraft/ folder, with almost 700 of those being AI planes.

Ever wonder how many duplications you have?
Being a bit of a neatnik I started looking at my AI folders and found a bunch of instances where I had different folders with identical models.
I was able to consolidate many to eliminate having duplicates.
An invaluable tool for this is called WinMerge -
http://winmerge.org/This great little utility compares files and folders on a binary level.
Say you have 2 AI folders for a 737-700. You can WinMerge the aircraft.cfg and the .mdl files in seconds and tell if they are the same. You can copy, say a [fltsim] section from one aircraft.cfg to another quickly.
Note: it will not present a readable version of the .mdl file, but you can easily see if two of them are identical or not.
Another Note: before consolidating your AI folders consider how it will affect automatic updates, such as WoAI installs.
I love this little utility and use it often.
Hope this helps.
cheers,
Joe
Don't argue with idiots, they drag you down to their level and beat you with experience.