Just had a look myself. Looks like a nice big batch of straight-up-uncompressed bone matrices near the beginning of the file, so that's good. I would have at least expected some quat compression, but I'm not complaining.

First thing to do is probably locate offset bits for the image location since it's a known piece of data. Wherever that offset is, there are probably more offsets to other meaningful mesh data.
Edit: Alright, I've been working on it over the past few hours. The file is broken up into chunks, and I've figured out how to ID the chunks, be they bone data, meshes, or textures. Mesh data is a more complicated matter. I'm using the crystal model as a simple test case.
Strangely, it draws the verts properly as a raw triangle list, but there is a data segment right before the verts that looks very much like triangle strip indices. However, trying to use that index list does not look correct in any way, so I'm not sure what the point is. It can't be a list of weight indices, because the crystal doesn't need to be weighted (since from what I can tell it only has a single root bone, and if every index were the same that would be obvious).
Vertex data is also not stored at all in native PSP GPU format. Vertex positions are offset from the beginning of the list before UV coordinates, which is not an accepted hardware format. However, vertex formats do vary wildly from model to model. I'm probbaly skipping over a format descriptor somewhere along the line.
As a side note, the very large files appear to be purely skeletal animation data with no mesh data at all. But many of the character model chunks also include some skeletal animation data.