Hm, interesting. The longest one I've ever had was around 10minutes. I woke up and looked at the clock, relaxed and got the sp, broke out and looked at the clock again, ten minutes had passed but it seemed like ages.
Are you guys sure its been lasting for 30minutes, cause it could just be the perception of time that changes. Not sure.
I also get the hallucinations, as you mentioned hop_ic. Once I saw shadows on the walls, walking around like they were humans on a light show. It was creepy and relaxing at the same time.

I'm wondering about dream inducing techniques during the SP's because everything I've tried so far wont help me. I'd like to try getting into the dream this way, because I can choose a place to start, other than the usual cafè routine I go through. I've tried mental humming (not vocal, just in my head), but its all forfeit as the sounds I get from SP are overwhelming.