I wrote a javascript file that does exactly what you mention, from Launchbar. You can take a screenshot, give it a file type, compression rate, etc and it auto gets the url and stores the image in a intelligent manner.
ie.
Key functionality: it uploads screenshot, files and stores them on ~/Dropbox/Public/screenshots/year/month/timestamp.jpg for screenshots and ~/Dropbox/Public/files/year/filename.ext for files.
However, what you propose seems interesting. I think I'll implement a variation of that for my script.
Cheers.