Actually, SPR and INT influence the damage of summons now.
If you check the information of ktos.neet on Sorcerer/Necromancer, you will find the following info on the skills : Create Shoggoth/Summoning
Summon Attack = Z x INT
Summon Defence = Z x SPR
SPR also adds % attack [I believe the kTest thread about the changes said something about 0,67% per SPR-point] and defence [?; not sure about this] to your summon, so obviously after a certain investment, SPR is better than INT, depending on you Summoning skills skilllevel.
By going full SPR you can practically skip adding skillpoints beyond the first into your summoning skill, while you can maintain some damage by investing skillpoints and boosting INT + getting some SPR via equipment, or go hybrid SPR/INT to counter the summoning costs and boost both spell damage and summon damage.
I believe that this is a really good change that opened Sorcerer/Necromancer for all builds instead of locking them behind only INT or only SPR.