I would run 106 magery for 100% success with 7th circle spells personally. Flamestrike, Chain Lightning, Meteor Swarm, Gate Travel, Mass Dispel -- all very useful abilities. Wraith Form + Corpse Skin + Chain Flamestrikes is going to be the bulk of a Necromage's DPS.
As for Meditation. I still find it useful, but it depends on the encounter. There are some encounters out there where you will not be able to Mana Drain in wraith form the whole time. Even when I do Barra... erm.. The Piper, I often run him out of mana with Flamestrikes and have nothing left to leech from him. I can typically switch to Fireball when this happens and still maintain some DPS on him. But no mana to drain = no sustain (especially with consume running).
Certain spawns will have waves with nothing to drain from either -- Semidar, Mephitis, and I think part of Rikktor all have parts or all of it where you can't leech from the spawn.
As useful as spellweaving and WoD are, Spellweaving is what I swap meditation with when I need it. I will also use meditation if I am doing content where my pet will be doing the bulk of the fighting and I need to supplemental heal a lot (Void Pool and Travesty come to mind).