Yes, you will hear a benefit from using better speaker cable between vintage gear and speakers, for the same reason you hear the difference with modern gear. Vintage vinyl insulated zip cord type speaker cable will reduce sound quality no matter what gear. Modern gear may have more resolution than vintage components, but the resolution of vintage gear is still far better than what vintage cable could deliver.
I would recommend replacing all the speaker cable inside and out with modern engineered speaker wire, like Canare 4S11, neotech, etc. The pure copper and non-PVC insulation will be worth the effort. Canare is not expensive.
BUT! There's always a BUT
Some vintage amplifiers had a bit of an "edge" to them which is tamed by other parts which deliberately throttle resolution to soften things up. Back then measurements were everything, but we know now that measurements don't fully describe the sound and feeling we perceive. So be careful replacing vintage parts, you might want to reinstall them if the modern upgrade parts are a little too revealing.
