Hi!
As proposed, I Deleted the Sponsor plan from the member account using the Subscriptions tab of that user within the Joomla back end > CB members.
This seemed to work as expected: The Sponsor subscription was removed, the Gold Sponsor subscription remained, and the overall Subscription tab for that member was updated to remove the extraneous subscription options. Also, the Joomla User Group granted to a Sponsor subscription was properly rolled back/removed from this member.
However, now this Gold Sponsor has no plan image. (Before, the plan image for the Sponsor subscription appeared for this account.) Any ideas for enabling the Gold Sponsor plan image?
Thanks again for your help!