Hmm. I'm thinking now my spellbook is flawed in that it doesn't take advantage of the Necromancer's poison immunity OR the fact that all of my creatures are non-living. Idol of Pestilence is a good addition that would take advantage of both of those things. And I was probably too hasty to remove Poison Gas Cloud.
Unfortunately, I am slammed with final exams all this week, so I won't be able to contribute anything to this forum. But I think I will try out various Necromancer spellbooks this weekend and post which one felt the strongest.
This is an interesting digression on the Focus vs. Versatility axis in the game which is rarely discussed.
Playing multiple copies of the same synergetic spells gives you Focus but at the expense of Versatility.
Where you pitch your camp is really a matter of personal style.
But if you want a book that's consistently good against all opposition, you need to have some Versatility.
Otherwise you're playing "match-up lottery", beaten by some nemesis builds and walking over others.
It may be rarely discussed but it is certainly something you always to have to think about. On one hand, you don't want to be a slave to your theme (a rule MtG players will be familiar with). On the other hand, if you lose focus of your theme you aren't building the best spellbook possible. I think part of the versatility comes with the standard spells that most spellbooks include: nullify, block, bear strength, hawkeye, seeking dispel, dispel, dissolve, teleport, force push, heal, etc.
One of the Necromancer's weaknesses is his defense and life-gain options. I almost included 1 Heal in my spellbook, but it took up too many points. Unfortunately, I hate Drain Life, so I was only left with Regrowth Belt, Deathlink, and 1 Vampirism for my mage. (Drain Soul might help in this area, but I haven't played with it yet so I don't want to jump to conclusions.)