Hi Per,
Yes, you're right, that's a good point. Full DB restore is certainly not suitable for sites that are already running online in the production phase. If you're adding modified documents to the live site that already has a "traffic" like newly registered users, forum posts, comments, statistics, all this would be reset. This approach can be used only for sites in development.
You may also write your own code that would update the document in the target database... however this is not very easy task, processing all the details that have to be considered. Some info can be found in Developer's Guide / API section:
Updating a document and maybe also
Using API and CMS Controls outside CMS project.
The approach with deleting the document and importing the new version looks easier when these changes are not frequent.
Best regards,
Zdenek C.