Try this as an experiment
Create a new file with your seed file, now reference attach one of the so called bad or suspect files use world coincedent and no nesting for a start... if nothing bad happens, fit view all and you if can see elements in the design plane and in the level view display manager ( it has column you may need to turn on used and elements)
this will at least let you know if the file actually has anything recoverable ) then select all and copy into the active file snap to a selected object so they dont move... now you should have a repaired file to replace the bad one..
We used to be able in V7 to run the Edg program from the dos command to repair & or analyse bad files.. this is no longer an available option in v8i...
I have not tried to use the Repair / verify option in V8i on a file that crashes utn and cant be opened but maybe the batch processor could be made to run the command over the bad file from inside a session of a good file... sounds like a good way around the lack of Axiom Repair tools kit ( 3rd party program to analyse and fix bad files) or EDG pre v8 tool from Bentley......