Gold Cart updates are a bit different... the best way seems to be:
1. Deactivate Gold Cart plugin
2. Delete old (outdated) Gold Cart plugin
3. Download newest Gold Cart plugin from GetShopped.org
4. Install 'new' Gold Cart plugin via upload (or FTP)
5. Reactivate Gold Cart.
6. Go make sure API Key shows Gold Cart is working using
There are web-pages out there that give the same sequence (strangely, not affiliated in any way with GetShopped... but apparently reputable nonetheless).
As for my problem: my 'domain' issue is fixed, and Gold Cart reports that it is registered correctly. I can setup (and see) 'Grid View' on my Store (so I know Gold Cart is working), but I still cannot 'Add Media' (an image) to any products (using Product->Edit). Products show a 'placeholder' (empty image) in lieu of a real image.
On Pages, Posts, tables, etc... the 'Add Media' button works just fine, grabbing and inserting images from my Media Gallery. But for some reason, I cannot get the 'Add Media' button to do ANYTHING at all with Products->Edit. Likewise, I cannot 'Manage Images' from the Product-edit page, as this button also does not appear to work. Frustrating....