Yo IABB (aka Fletch),
I can answer some of your questions, but have a few of my own for when others jump in.
In some ways GBase is replacing Froogle and in others it is not. If you want to your products listed in Froogle, Google (sometimes lists Froogle products at the top of listings) and other "Google search properties", than you must submit them to Gbase. Froogle no longer accepts direct submissions.
Now Google also admits that they do not expect shoppers to visit GBase directly, nor do they have any plans on marketing it to accomplish this. It seems that its purpose is to manage your product listings and data feeds so that Google can distribute them to other web destinations like Froogle.
At the same time Google is de-emphisizing Froogle and it seems as if changes are in it's future. However it still exists, and..... When Google lists "Product Search Reslts..." at the top of their SERPs these listings are coming from Froogle not Gbase.
General "on-page" seo seems to go a long way within the Froogle/Gbase system. But I would love to here from others on optimization techniques.
Also, my big question for the group is this......
How often does froogle update its results to reflect Gbase? I have made some changes to my feed lately and have gotten several #1 spots in Gbase. However, in froogle I am still on pages 4-20.