Hello,
Content staging distinguishes between global objects and content - documents, etc...
Description of what is synchronized is in
DevGuide staging overview articleStaging module logs content changes and object changes separately.
Document types, templates and layouts are global objects. The content (text in editable webparts etc.) is bound with the document and is logged as content change.
Therefore, if you setup logging object changes in your Dev site only, and setup logging of content changes in QA, then it would generally fit your needs.
The content won't be affected after update of page template or layout, unless you change the IDs of the content webparts. Even if you do that, content will be preserved, however you would need to restore the former webpart (with appropriate ID) to get the content back for any usage.
You may want to create some documents (with or without content) in your Dev environment in order to create the content structure... then you would need to enable logging of content changes in Dev env. too, and later synchronize only object changes.
Another option would be
Bi-directional staging so that you could modify the layouts etc. with up-to-date content from QA. You can analyse your processes and choose the setup that would fit your needs.
Should you need any additional details, please feel free to ask.
Regards,
Zdenek C.