Originally Posted by
Antipodes
Unless it's by a well-known manufacturer where keeping it in its original state might be important (unlikely) the rule of thumb for most antiques (not musical instruments however) is it needs to look like new or close to.
But most serious restorers would also say use all original material where possible and practical. The dowel is easy to replace, re-blocking chairs is comparatively simple with some patience and rubber mallet to gently take them apart, animal glue will be easier to work with and also make it easier for future restorers to not have to pick off impossible to remove modern adhesives.
It's not that difficult to salvage and re-use horsehair (you just shampoo it like hair), replacement hessian and the other fixings are all reasonably available.
I'd say your biggest decision is if it's worth the effort - a lot will depend on how unique or simple the piece is, how much you and yours love the piece (it sounds like there's a strong family connection), etc, etc.
About 100 years old could put it a few places stylistically so would be good to see photos. Art nouveau (aka Federation), Art Deco and later are pretty safe. Anything much earlier than that can be a problem.
I'm not a dealer but I'm a knowledgable punter and I'm noticing and hearing from dealers (in big cities at least) that 19th century furniture or stuff in the manner of (even really nice locally produced cedar furniture) unless it has Biedermeyer-like proto-modernist simplicity, is very difficult to get rid of. People just aren't interested and think it's too busy and heavy for a modern home.
Obviously we're in the middle of big mid-century trend right now but, even expecting that will die down, I think anything pre-Federation will be difficult for a long time.
If you dig the C19 stuff however, it's probably a great time to be buying up resto jobs.