Suzy, the same person who originally owned Brock’s Vulpix, had a friend Zane who owned Ninetales. Brock was also confused for an ancient Ninetales’ old master as it tried to convince Brock to stay with it. Brock just seems to have a thing for getting involved with this pokemon family . I think the joke here was that Ninetales and Vulpix were supposed to be the beautiful pokemon of Kanto, and perhaps the rest of the world, Brock has a thing for beauty and so of course he would get tangled up in situations with these two.
WHY YOU WANT A NINETALES
Ninetales was a pokemon you could only get if you happened to have pokemon blue and decided you want to catch a Vulpix. For the rarity factor alone Ninetales was worth the capture. If you got up to the Flamethrower move with your Vulpix, if you could be patient enough to wait for this beauty of a pokemon, than Ninetales improved stats could actually be worth it.
WHY YOU DO NOT WANT A NINETALES
Ninetales suffers from evolutionary stone-itis. It doesn’t get moves other than the ones Vulpix gives it, and that can bite the big one if you caught a Vulpix went to Celadon and bought a fire stone, and then evolved your cute new pokemon into a useless Ninetales that would only know Ember. And for the most beautiful pokemon in existence its sprite definitely didn’t show it. Though I will admit the sprite for it in yellow is worlds better.
IN SUMMARY