John, thanks for your reply!
I find it unlikely that my system would be having any sort of performance issues given its capability - but I did disable animations. No dice.
Then I restarted and tried to use Dropzone again. Still incredibly slow...
Fully uninstalled the Dropzone that was downloaded from the App Store and reinstalled using your link. This worked. I now feel comfortable enough to play with Dropzone and add some user actions. If I have more performance issues, I will update and let you know. Thanks again!
Also - what are the implications here? Should I not trust further updates from the Mac App Store for Dropzone? Is there some larger issue with the App Store that I haven't heard of before where your uploads are corrupt? Any idea what the issue is the with App Store versions?