In high mp7-10 SV/ROE/BR SV->save death
In low MP 3-5 GI/RoE/BR SV->makes little sense
In ultra low MP 0-2 SV/GI/BR- SV>move faster
I'm close in opinions. I don't use SV in high MP because I'm under the belief that if I'm about to die its because I screwed up... and I do everything in my power to not screw up :P
High MP I run with BR/SA and RoE or GF depending on what I feel like playing. A lot of people dont like GF for higher MP but I still love it since I have a high enough DPS I can clear trash mobs pretty quickly, and having those floating mana bubbles is amazing for elite fights.
I'd say SV is useless on higher MP, if you are geared. If you are undergeared and relying on a passive to save your !@# once in a while then yeah I guess it's OK to use... but as far as utility in higher MP... there's better passives.
Now, in terms of low MP farming for fast paragon / legendary runs... Spirit Vessel is amazing. 2 seconds reduced on Horrify (Stalker) and Spirit Walk (Jaunt) makes for some SERIOUS mobility when combined with Grave Injustice. Nothing to argue there.
Mid-Range MP settings can be kind of tricky. I'm not sure what my current gear will show... but when I run mid-high range MP I have almost 80k hp (swap innas pants for blackthornes w/ 230 vita + 12% life) and the Blood Ritual passive gives me 800 life regen. This is such an amazing passive... and I'll take this over Spirit Vessel any day. I usually always run with Spiritual Attunement and Gruesome Feast in mid-high range MP settings... so the swing here would be having either Blood Ritual or Spirit Vessel... and again, it's just not worth using a passive slot because I've either been lazy or careless and am banking on the passive to save my $%^.
Those are my thoughts.
Spirit Vessel in my experience only seems useful in MP0-2 for mobility. Reduced cooldowns on both the WD's mobility skills is HUGE when combined with Grave Injustice. As far as higher MP settings are concerned... there is definitely better passives to choose from (Blood Ritual, Spiritual Attune, Gruesome Feast, Jungle Fort, Pierce the Veil)
It really depends, for act 3, SV saves me from a fallen maniac at the last second EVERY time :)
You have 300 vita. I'm sure spirit vessel is useful for someone terribly undergeared... but in terms of endgame usage, it's not the best passive (other then for speed farming)