I really like the one in the original post. Its easy to get too much antique furniture with hopes of restoring it so you do have to be fussy unless you can afford to hire it out.
I wonder if those "original brass wheels" belong. maybe someone just drilled holes and stuck some old wheels in there?
The others are a bit too ornate for my tastes but nice.
Leather seems like a likely alternative to the horsehair, but if you can find suitable upholstery, why not.
smells, well if you were intending to strip and do a proper ground up restoration than I wouldn't fear the wood holding onto smells and you'd probably replace the rest. reuse the springs. heck they used to bury the wood in horse dung because they liked the look it gave the wood. I think they still make horsehair
It's quite a project though. neat to see.
I think its the sort of thing you could fall in love with and spend oodles of time to restore and be proud of. If you are so inclined then you might also buy a lot of other antiques and swamp yourself in projects. If you pay someone else to restore it then you could probably expect a big price unless you know someone specifically that would take it on. hopefully someone that doesn't suggest foam or use a glue gun
maybe there is merit in just leaving it as is give it a good cleaning and enjoy it for what it is? patch what's necessary and call it an antique?
maybe some things like this , that are rare and original would see an increase in price as there are so many that would buy it and do a novice attempt at recovering it. Antiques seem to be at an all time low but they don't make them anymore so perhaps in years prices will go up? ( supply and demand changes) I'm not seeing that effect with my old radios. They just don't interest most younger people. Maybe furniture is different.