Thanks for the reminder … I think starting your post “along the same lines …” may have confused people who would otherwise responded.
Forget about suing anyone for anything. Try to take the emotion out of the situation and identify how you have been disadvantaged by the decisions made by the committee and then ask that you be excluded from paying for any of the repairs.
When they refuse – as they almost certainly will – take the owners corp to NCAT seeking reparation that excludes you from paying the resultant special levies.
If you have evidence that the downstairs neighbour has changed the layout of their unit, report this to your local council as that would require planning permission, not to mention special resolution by-laws relating to common property.