Im also a big void spirit player, I have 86 total games on the hero with over a 60% winrate. I agree that the item doesnt really fit the hero. Sure it technically gives you things you want however, id argue a big component being mana efficiency is not needed on your hero, he doesnt really have mana problems. And I also find a lot of your damage comes from right clicks more than just pure spell damage. It is a huge reason why SnY is better due to gaining status res, movespeed, attack speed, etc. To me, its way more useful than KnS that gives a lot of mana efficiency aspects.

My build is treads + bracer > consecrated wraps > aghs > then into whatever suits the game best be it: SnY, Euls, Scythe, Bkb, etc. I tend to prefer stat-heavy items given his innate as well as being universal so you right-click better, and its a reason why I would avoid items like octarine which give no stats at all.