Hey!
I just recently had a problem like yours with Cpu spikes with 7.5.30 on mac os x 10.9.1. The real-time peak meter was going to the max with not that much plugins used.
So I disabled internet for Cubase and almost all spikes disappeared. I freezed some vst synths and the spikes disappeared fully.
Weird, I guess there is a synth trying to connect to the internet or something and was malfunctioning. Now i just have to find out which one!
I have also seen on the Pro tools forums that you should disable the multi core function in Kontakt 5 because it makes spikes, its not anything i have tried yet but maybe that might work?