I may be wrong, but I thought that Spell Foci in Necromancy would reduce the summoning point costs for the Spirit theme? I have GSF Necromancy and summon 1 costs 10 and summon 2 costs 30. Seems to be a bug.
I'm almost positive that is because summon creature is directly keyed to conjuration whereas animate dead is necromancy. Personally I didn't think it was going to work when I last tried and tbh i'm not surprised. Also I don't know what work it takes for the DMs to change that or if it's that worthwhile to do it.
I'm pretty sure SF and GSF necromancy only works on animations, not conjured spirits.
You can see the effect of SF And GSF here http://www.escapefromunderdark.com/forums/showthread.php?t=49389
This is the only SF that seems to effect summons.
QuoteSummon duration has been reduced to 4 rounds/level for vanilla casting, 5 rounds/level for SF: Conjuration and the usual 6 rounds/level for GSF: Conjuration (i.e. casters with GSF: Conjuration will, for the most part, be unaffected by this change). To compensate for losing transmutation spells for spell school specialization: conjuration, this will grant an additional 2 rounds/level duration on summoning spells.
SF Necromancy does effect animating.
There's also some perks that effect summon points and summon duration.