We've been working on a tool that can make data-entry easier if there are existing records that the new records could be based on. (Sort of like copy-cataloging in the context of a library.) I'm not sure how broadly useful it may be, but I've set up a demo integration with Omeka:
http://firuta.huh.harvard.edu:8080/fp-omeka-demo/
Let me know if you have any questions.
We're not doing our metadata creation in Omeka, but on the (test) platform we are using, copy-cataloging is one of the most requested features. If you were to share a plug-in that offers copy-cataloging, I bet there are folks who'd appreciate it.
The plugin should work for most cataloging web applications. There's a readme at https://sourceforge.net/p/filteredpush/svn/HEAD/tree/trunk/FP-DataEntry/.
(If you'd like me to set up a quick demo so you can tell whether this is worth your time, I'd be glad to. Perhaps email me a url and a test login? cmccallum {at} fas.harvard.edu.)