.I'm sad to announce that apparently both automatic IVTC methods I found failed and manual IVTC still seems to be the only way to go with the VHS sources. However, I am progressing nicely in the filterchain of the DVD sources: pretty much all of the HORRIBLE rainbowing has been removed and I might have found a way to remove (or at least dampen to almost unnoticeable status) the NASTY haloing without killing details and sharpness in the process.
Everyone: please try to contribute. There are lots of things you can do without having to create subtitles or do manual IVTC, none of which consumes more than 5 minutes a day.