salam
manta is core item for spectre for the reasons you already know. And buying manta and SnY in same game is waste of gold. just buy manta and diffusal blade.
SnY on Spectre used to be a thing for a short while when she was first released in 6.28 or 6.29. I stopped playing Dota around 6.5x and when I got back to it years later, I was informed in no uncertain terms that I could go kill myself when I built SnY on Spec.
I think back then Manta didn't work like how it does now, it didn't give you +ms, instead it gave you Diffu's manaburn, just larger amount (iirc 36 manaburn instead of 18).
But when the Manta change happened, SnY became an obvious inferior choice.
კომენტარის დასაწერად გაიარეთ ავტორიზაცია.
We all know Spectre benefits greatly from Agility because her illusions gain attack speed and can land more attacks with "Desolate" (and dmg+armor of course). We also know that she needs Strength for her tankiness and "disperse". Also Spectre is a Chasing hero who needs as much movespeed as she can while also needing means to slow the enemy.
I never tried SnY on Spectre myself but everything SnY gives seems to be what Spectre needs. discuss