I did some really basic math using my spread sheet. I ripped out thunder from the rotation, figured the DPS out, and I think according to the numbers I am using Spell Speed goes from about an average of 0.015% DPS increase per Spell Speed at around 100 Spell Speed, to about 0.017% average per Spell Speed around 100 Spell Speed.

This in comparison to about .034% DPS per Crit, .04% Per Det, and .2% Per INT. So its more important, but nothing that ground breaking.