The CsvImport plugin provides a pretty good way to do this; it's a little complicated to create one item with multiple images, but better by far than relying on Dropbox.
Basically, you're using OpenOffice Calc, or whatever, as a faster metadata editor. Judicious use of formulas makes it easier (enabling automatic duplication of a column for "Creator" to the Zotero column for "Author", for example.) It's harder to scale this to thousands of items without making one's brain bleed, but in the dozens-and-hundreds-of-items scale, it's not too bad.
As of this writing, I've got a basic OpenOffice Calc file posted on my server's temp directory; see http://cliotropic.org/tmp/omeka/Whipper-TX-1928.ods. Feel free to take a look at it, export it to CSV, and import it to test things out. (That file and the images it points to won't be there forever, but they'll be there for the next few days at least.) If you've got any questions, I can try to help.
If I weren't busy writing a dissertation, I'd start drafting a best-practices guide for how to do this time-efficiently with a research collection. Maybe someday.