That's just pointless.
Wow, my icon is 50x bigger than my other icon, it must be more important. That's gonna be a organizing nightmare and that's never how a real desktop is presented (do you put your important documents in a bigger folder?)
There should just be a different type of folder icon that's more "important" looking than others.
It's not pointless. In every folder there are some files that are more significant than others, and users do not, generally, like spending hours making new folders and moving files to them, especially if you're trying to collect related files in one place.
If you're creating a document, for instance, the chances are you want things like the images and notes to be in the same place as the document itself, and probably the output (as HTML, PDF, etc) there too. It's intuitive. All of these are related, why should you spend ages building sub-folders and patiently moving stuff to and from them?
At the same time though, you don't want to open the folder and immediately have to look through a hundred similar looking icons to find the actual Document.
In a spacial environment, with this feature enabled, you can easily organize the folder so there are no scrollbars and everything is right there. The support files would be clustered together and fairly small. The output files, the ones taking the final published form of the document, HTML, PDF, etc, would be larger and clustered together. Alternative versions of the main document would also be larger and clustered together, arranged in a row. And finally, the document itself, the thing you're most likely to want to edit, that would have the largest icon, right there in the middle of the window representing the folder.
Myself, I think a more interesting technology would be one that makes all of this automatic. Anything dragged into the window would have one, very small, size, and clustered with other dragged-in files. The Word Processor would use settings associated with the folder to set the icon of the main document to be "Main document" size and located somewhere in the middle. It would also cluster the outputted publishable files and set their size, as it would back-ups and alternate-versions.
It's an interesting technology that could be very, very, useful, if the UI to it is sensibly written.