Hi Forrest,
Thank you for your question. This is a limitation of the system by design. There is no way to reuse images saved as the primary image for Wiki, Category or Item pages.
Dozuki compresses all site images, which are delivered via a content delivery network with servers around the world to ensure optimal page loading no matter the location. The potential for increased page load time due to this limitation is extremely minimal and should not affect the functionality of any of your site pages.
If you have any other questions or concerns, feel free to email us directly at support@dozuki.com. Thank you!