I could give a long and winding explanantion, but the best explanation is that Methamphetamine is a more potent version of the parent drug, Amphetamine. It's not necessarily a proportional difference, like say, Beer to Liquor, in which the only real difference is a higher proportion of total Alcohol in the solution. Methamphetamine, in fact, works differently on the body and mind than Amphetamine. It tends to be more cerebral, with less physical side effects (which often leads to higher total dosages of Meth being used comparatively) and longer-lasting.
I feel like the lack of physical side effects relative to non-methylated Amphetamines leads to that redosing behavior and ultimately to a higher chance of psychosis and general insanity. Yes, you could use a little bit of Methamphetamine, cut the experience off at bed time and turn off your night light, but that's not generally how these things play out. You will likely end up misjudging and using more Methamphetamine than your sober-self would have ever given the okay too. You might not use all of that Meth, but not for lack of trying. A half a gram for a relatively naive user is enough for probably a week without sleep.
The thought of using Psychedelics with Methamphetamine makes my spirity cry out to the universe in pain. That's like forcing something fucked up into something that's pretty much perfect. I don't even know how to explain it. There aren't really any health issues involved, I just think you will be robbing yourself of spiritual benefit by using it with potent stimulants, but this is totally my opinion.
