Using Google docs is a great idea!
I will do this myself too, just a couple of questions if you do not mind:
1) How often did you set the Periodic import on the feed importers settings page?
2) As Google docs requires a login I take it you have set permissions so the spreadsheet is in effect online via a url? Did you simply publish it to the web and tick the box "Automatically republish when changes are made" ?
Would be a great help to me before I decide to use google docs for this.