Welcome to the Nexus Cayotic!  Your attitude towards DMT seems like a healthy one.

It's very unlikely that those "Spice" products you bought had any DMT in them.  "Spice" is a generic name for herbs laced with synthetic cannabinoid agonists... chemicals that mimic the action of THC.  The one that gave you a bad trip was probably either exceptionally potent, or contained a chemical to which you're particularly susceptible.  It's not likely that a head shop would sell a mix containing a schedule I drug instead of a cheaper unscheduled chemical.

The fact that both DMT and these shady "legal high" research chemicals have been called "spice" appears to be a coincidence.

That speculation is outdated.  Well, at least half of it is.  The part about DMT being secreted from the pineal gland was Strassman's speculation.  But it turns out that the pineal gland doesn't express the mRNA for INMT (indolethylamine-N-methyltransferase), an enzyme that is required for the biosynthesis of DMT.  This mRNA for this enzyme does occur in the lungs (and some other tissues that are escaping my memory at the moment), but not in the pineal.  The part about DMT being involved in dreaming was Jace Callaway's speculation... and to this day it remains only speculation, without any significant evidence to substantiate it.  It's not impossible that this might be the case, but I'd like to see at least a bit of evidence consistent with the hypothesis considering how often it's thrown around.

Documented where?  I try to keep my ear to the ground, but last I knew this was Strassman's personal pipedream, founded on wishful thinking in the absence of evidence.