While the melting point of Mirtazapine maybe low (116 °C) its boiling point is really high (432 °C) and I doubt maleate or hydrochloride salts would be much different. Inhaling all that vape junk from the fillers, binders, outer coating etc. in the vane hope of getting some enhanced effect seems a bit out there to me.
It's a who knows, when it comes to what pyrolysis/decomp products are giving you these effects, placebo or otherwise. What I can say is this is definitely not something anyone should doing or recommending to others without first extracting the drug from the pills.