Okay, maybe this helps.
As I understand the OpenACS object system, currently to add permissions control etc to the SSP for each cell of a spreadsheet, one would add cell.object_id and table.object_id to the above properties, where cell.object_id would inherit from table.object_id. Cell level control becomes important, for instance, with bookkeeping data.
Yet, creating each cell as an object would be overkill, because it's essentially an attribute of the table.object_id. Perhaps the AMS would be an appropriate use here, changing cell.object_id to cell.attribute_id or cell.attribute_type... whatever.
Maybe this is.. probably is.. way out there. I'll be quite now.. =)