I think SDM is SteroData Maker:
StereoData Maker It is based on CHDK--and optimized for connecting two cameras next to each other for stereo photography... It does use the USB switch (just like you did) to sync trigger the cameras (perhaps with out needing a basic script to run???). Not sure it would have any other advantages for you. (whoops, missed that cybercom posted the link to SDM...)...
And, as far as I know, there is only one model of A570/A570IS--it is the same camera--people occasionally drop the "IS" (Image Stabilization) because it is redundant when identifying the camera model.
Sorry to answer the wrong question about power consumption--but I think you have it nailed already.
Look'n good!
-Bill