From my experience, and from what I have heard from others here, it seems to be very similar to the motivation behind reading a book. Love, and lust, can be defined as emotions and therefore they can be expressed via text in the same way as any other emotion.
I guess what I'm trying to say is the key to it is not so much the act of cyber-sex, it's all in your imagination. Which is why, in my opinion, different people have different experiences and ideas about it. Someone who doesn't wank without watching porn would likely think it to be a pointless endeavour. Whereas someone who can give themselves a boner with a thought would probably find it a lot more rewarding.
In the end I think this experiment will tell you a lot more about yourself as a person, rather than the rewards of cyber-sex. Good luck with it though, I'll be subscribing this thread.