Typically old binary; unfortunately these are the documents which clients' accounting and legal departments tend to send me. OOXML is better, though not always identical to the Word rendering. Spreadsheets, in fairness, tend to do pretty well.
Bug reports: no. I do participate in open source projects, but I really just want to pay someone else for an office suite.
You could probably pay for someone to fix the few rendering/incompatible issues with those old binary formats as a patch. Any paid solution would likely have similar issues, so paying for the functionally you want/need directly is likely the only alternative to just using Word directly, and you could give back to the community in a big way if that's something you value. It might cost as little as $200 or so.
The problem is I think so few people care about those old binary formats these days, so there probably isn't much demand to improve compatibility for the edge cases you are encountering.
Old binary word docs or recent OOXML based ones? Do you file bug reports?