horsehair plaster?
Answers:
You can keep the same look by covering them with 1/4" drywall and skim-coating the entire wall. This will give the same look as the original hand-troweled plaster, but give you a sturdier wall surface.
If you don't cover the plaster with wallpaper, you will be chasing cracks forever. There may be some stabilizing treatment that can be applied to the plaster before painting, though, but I don't know any offhand.
Other answers:
Our 1873 farmhouse has the horsehair plaster walls also. We love the character it shows. We painted it with a semi-flat paint (using different colors in each room). Keep it a semi-flat or otherwise it will show the dips and curves in the walls. What we did in the kitchen is painted the top half of the walls and use bead board with a 4" flat baseboard on the bottom of the beadboard and a lip molding on the top. We stained that. Turned out really nice.
Our 1873 farmhouse has the horsehair plaster walls also. We love the character it shows. We painted it with a semi-flat paint (using different colors in each room). Keep it a semi-flat or otherwise it will show the dips and curves in the walls. What we did in the kitchen is painted the top half of the walls and use bead board with a 4" flat baseboard on the bottom of the beadboard and a lip molding on the top. We stained that. Turned out really nice.