The value of your furniture is based on:

Quality - Upholstery should be built of hard woods like maple or oak.  Poplar is OK.

The frame should be at least 1" thick.  Feel the bottom edge of the sofa.  Is it over an inch thick?

The frame should have doweled joinery with corner blocks for reinforcement.  Feel for corner blocks underneath the sofa.

The springs should be tied with an "8-way hand tied" technique to create a stable and firm deck.

Does the piece have enough padding?  Do you feel the hard edges of the frame around the arms?  Do you feel the spring coils under the seat cushions?

If you can screw the legs on and off, it's probably not worth reupholstering the piece.

Personal or Sentimental Value - No one can put a price on this other than you.  Just know this... antiques are over 100 years old. Valuable antiques were originally made of high quality or are unique or rare.  

Some "designer" type furniture, for example furniture by Le Corbusier or manufacturers like Herman Miller are highly valued even though they're not over 100 years old. What makes them valuable is there iconic status for a given period of style, art, or architecture.

Past & Present Furniture Manufacturers That Have Built Quality Frames:
Widdicomb - Baker - Henredon - Dunbar - Hickory - Bernhardt - Ethan Allen - Ashley Manor - Beachley - Sherrill - Harden - Stanley - Century - Stickley - Hekman - Hickory White - Flexsteel - Steelcase - Knoll - Cumberland - La-Z-Boy - Lane (before the 80's) - Broyhill (before the 80's)