First, I do not use Aperture, nor have I ever used Aperture. But I have a customer I print for who sent me some files via Dropbox. He uses Aperture 3. I use Dropbox all the time and have never had a problem with folks sending original files at the original size, not compressed.
So, this customer sent me 6 files or so, and I received them zipped together in Dropbox. I have no idea what he did or what settings he used, just that the original file sizes were like 80-135 mb each, but the files I received after they were unzipped were more like 8-20mb each.
I'm trying to help the guy, but it's a program I am 100% not familiar with. Maybe some export setting in Aperture? Maybe some upload setting in Dropbox?
My advice to him was to work on his files individually in his software, safe each one as a TIFF, then upload each file individually to Dropbox (not a folder full of images). Or better yet, just bring me a disk or flash drive.
Still, if there something obvious to look for, I would like to point him in the right direction without spending too much time learning about a program I'll never use.