While buying a more modern dual-pivot caliper would improve the power of your braking, I find that people often forget to clean their rims from time-to-time. Over time, the brake pad rubber will embed in the rim surface making the brakes less effective. You may not even notice it, but you would be amazed at how much black comes off the braking surface if you clean them with some rubbing alcohol and a scouring pad, or even wet sand them with a fine sandpaper. I'd go with new pads made of a soft rubber such as the salmon colored Koolstop pads, clean the rim braking surface, make sure the wheels are true, and adjust the brakes properly before buying new brakes.