People like to be right, but lets think about what the 'net' of the situation is. Most theistic Satanists are doing self-deification work as well much in the way of the LaVeyists. I can see these people easily existing within the breadth of Church of Satan because they are in agreement on every major point and practice mostly.
Well the Church of Satan was founded by Anton LaVey, that is why theists are separate from the non-theists. They are separate because of their disagreements.
In fact, I really couldn't see a reason why they would be practically incompatible and atheist Satanist could be standing in the same room doing a ritual with them and the mentally of both would be the only different thing. One may see this as just a psychodrama, the other believes in the meaning of the words. At this point it's just artistic expression! Poetry vs Psychology.
I can understand this part, the ritual is for the phsychodramtic effect and adds confidence to the belief. After all my demon did chose me by flame, and through ritual .
Theism really is working magic through adoration as much as will, and it doesn't really change the mode of working just the heart in it. The mode of working that is best for you is the one that you naturally have affinity for it doesn't really matter what others think of it and certainly there is no quality comparison either. Both work... Remember, the theist is just as likely to be quoting Nietzsche and Ayn Rand as you are.
I do agree with you there, the relationship between the mind and Satan or simply just the mind is greater than any other...in most cases.
Honestly, I see theism more attractive to left brain types for this reason. Again, not a value judgment just my observation. Even the non-theists in Church of Satan are not so polar about beliefs (this polarity is honestly Peter Gilmore's slant, and is recent.) and there is strict atheism to outright agnosticism in that organization depending on who you talk to. Remember, they give anyone who pays a card. You're not going to be refused on this basis.
I don't agree that theism has anything to do with left or right brain types, it has to do with irrational faith and supernatural belief. Again though, the CoS is founded on Athiestic belief, that is where the Setians became the Setians and Anton LaVey founded the CoS.
We all need to step back and get a little more perspective it's far easier to draw lines in the sand than to just accept a little variance and realize you are all on the same team.