I do keep my collections in my collections folder in my main "scrapping supplies" folder. So if I search "staple" it will find them whether they are in a collection folder or my embellishment folder (where say, a freebie staple may be filed...) I wouldn't take time moving files just yet. (or ever maybe)
When you find something you want to use in picasa, you can right click on it and then choose a few options. If you choose "locate on disk" it will open the folder that contains the item. So, if I find that staple and it is part of a collection, it opens the whole folder and I can grab that staple along with other coordinating pieces.
This is the sort of thing I was thinking about. I get the searching on keyword, but at the moment I am mostly using papers for my P365 layouts and like to see them in kits. In PSE as I have an album for each collection I don't need to think about what collections and the suitable keyword to use. If I rearrange the my folders into collections it would work in a similar way as I'd see the folder names on the left hand side.