Looking at the pictures you posted I can imagine what those brakes feel like in their current state. You should definitely get new cables and housing, read up on proper cable routing here: Cables

Get some Kool Stop salmon pads too, those ones are toast. If you want to make them feel better take the calipers apart, clean and grease all pivot points. Your brakes will never feel as good as a modern dual pivot set but you can at least get acceptable stopping power from them. I have a similar set of Dia-Compes on an 80s Panasonic and they work great.