I have not got a copy of the first DS game to hand but the second one appears to have a bunch of .dat in the sc directory, no compression seems to be there and the headers do not appear to have much (though I have not spent time looking properly at this point). Wider formats seem to be in (set the width in crystaltile2 to 128 or 256 until you know better for a given image) and a mix of GBA4bpp and GBA8bpp formats (fairly even split it would seem).
I have a bunch of portraits in f_edr05.dat, those mostly appear to be artwork rather than the in game sprites (which are actually backgrounds according to desmume, however Konami are not noted for doing things well on the GBA and DS).
f_fbrau00 and 01 have some more images, as do many other things that start with f_f
There are a few 3d models abused as 2d animations of a sort in the second game, however firing those through a texture viewer says most are minor animations or backgrounds.
I am still working on the palettes (the image below has the wrong one is the viewer)
Anyway one imagehttp://imgur.com/V8aEeps