They do share potential similarities, however, in the 975 RP tier, we're usually looking at new particles/sound effects where needed, and a recall animation.
A good example of this would be with Arclight Vayne (975 RP) where only necessary particles/sounds were changed, as compared to Arcade Sona (1350 RP) where we changed all particles, and gave her all new sound effects. Some skins only need new particles, whereas others need sounds, too, because we've completely changed the weapon.
The rules aren't hard and fast - we price each skin on a case by case basis - which is why there is the 'sometimes' category.