The 3do/mat-mappings are done in the .cos-files iirc, those are purely text in Grim, so gleaming information from them is just a matter of reading. (It is also a nice place to start for finding out which 3dos belong to which costume). Even a few comments are still in those files, so they should be quite readable.
As for extracting only MAT/CMP-files, that should just be a matter of adding a filter to any current tool, a simple matter of minutes, although IIRC there exists no tool to replace single files in the LABs right now, only to create new ones (correct me if I'm wrong).
As for support for video, currently ResidualVM supports Bink and SMUSH, with MPEG2-support started (although probably not working right now, as the only proper testing-platform for that is Escape From Monkey Island for PS2, which doesn't get much further than the "Press Start"-screen BEFORE the intro-video.) I did do some testing back when support was added, by making the EFMI-demo use the MPEG-decoder on a video I picked at random, but that isn't much of a test. (Besides support there might have been broken by the recent rewrites in the movie-systems, which I didn't care to test heavily, as MPEG2 didn't really work that well the first time around, and probably needs a rewrite anyhow, whenever it's actually testable in some engine).
There is one problem with recoding them though, the current system in ResidualVM selects codec purely on Game/Platform, not by the actual format of video (which makes sense, what game suddenly changes it's codecs?
) Switching for testing is a simple matter (Replace CreateSmushPlayer with Create*****Player in grim.cpp). Do tell if you plan to do any such work beforehand though, so I can have a chance to test/fix the MPEG2-wrapper
(Oh, and for that matter, the current implementation is really quite friendly towards most of the ScummVM-codecs (scummvm/video), so adding in any of those (although not in the main-fork of ResidualVM) shouldn't be much work either).
As for any texture-work, all work should be done with 24-bit in mind, as TGA-support will be added down the line (for EFMI), with .SUR-files for animated textures, .SUR-files are simply textfiles listing TGAs. And the TGAs in question are 24-bit uncompressed. This _MIGHT_ eventually remove the need for the .CMP-work in some cases. (But I can't say for sure though before I've tried and tested it).