Importing a feed from a filefield?
well bottomline is:

You want to import a spreadsheet (maybe with multiple sheets in it) on a regulary basis.

I'd suggest the module migrate, you find the possiblility to import csv-files (and also an example if i remember right).

Migrate has maybe a little more effort in the start, but it also has many nice features like a hightwatermark, means if there is a counter or a timestamp in your file (for each record), then migrate can skip easily over former imported items.

Also tranformation of data is (if neccessary) with migrate possible.

At least you should have a close look at the module migrate.