I think the fact that the files are there with the same sizes means you could attack this more easily. All of my digital pictures are about 1.5-1.6 MB. Suppose you had two dozen spreadsheets, all around 25k, and they all have the same information in their header (like some sort of xml doctype declaration for example). You could make some assumptions and go after the key using that.
I don't know about loop-aes but I would like to see everything encrypted, even the linked list for the file blocks, so that a fragmented file looks even harder to read because you can't follow its bits sequentially until you break the code.
However I really do like the backup feature. I'm going to look into using this at work on Solaris. We have some files with encrypted passwords in them.