As a workaround for content templates you could alter the stored procedure mp_ContentTemplate_SelectAll so that it does not use the SiteGuid parameter and just brings back all templates for all sites.
If your sites use the same images and you have control of the server, a workaround would be to create folder /Data/commonmedia
Then copy all the files and folders from /Data/Sites/[SiteID]/media into the commonmedia folder
Then delete the media folder from each site under /Data/Sites/[SiteID]/
Then create an IIS virtual directory for each site at /Data/Sites/[SiteID]/media and make each virtual directory point to the /Data/commonmedia folder
That way all the sites have a media folder but they all really point to the same physical folder.
Hope that helps,