|I must start by making an apology. I thought that 'used for' information was displayed on mouse over an item by the default UI. I had completly forgotton that I have an addon called Informant.
Now I am not sure weather you are interested in making looter dependant on having informant present, I guess you would not be happy with that.
However you might consider checking to see if informant is present, and if it is, acess its 'used for' data for an item. That would remove the need for a loot list, if you wanted to pick up all the say alchemy raw materials, both primary and secondary. Used in conjunction with item values this could make a really fast low memory version of looter, assuming you lock out the on demand addon(s) for professions/gathering.
My thinking is, if someone else has provided data that you could use, it might be worth taking a look at.
Another idea is, since informant is GNU GPL (not sure what that is), if the licence allows; use their method for obtaining 'used for' data within looter itself.
Informant has two dependancies;
EnhToolTip - used for display purposes (only ?), and
Stubby - used to enable on-demand addons to load depending on events.
I guess EnhToolTip would not be required? as you would not 'need' to display additional information for looter to do its thing. Might be a nice or suggestable addon to work with looter.
As for Stubby, either it could be used as is, or you might be able to take a peek at its code and see how someone else has gone about using on-demand addons.