Shirdi Devotee can also take train from Nasik. If CR introduce Rajdhani train via Kalyan, Nasik is confirmed halt for that Rajdhani. Manmad is Important junction, but Nasik is bigger city. Mumbai , Pune & Nasik formed Golden Triangle of Maharshtra.
I have nothing against Manmad. But if you observe halt pattern of CR trains then every important & Super Fast train like LTT-NZM AC, PUNE-Kamakhya Suvidha, Geetanjali Express,LTT Haridwar AC Express, etc major trains are halt at Nasik & Skipping Manmad. (Though there are few trains like LTT- Puri which skips Nasik & halt at Manmand but very few).