I think you're right. Mephedrone brought a new quality. It's a type of euphoric stimulant that allows -at least for a stretch of time- to engage in an abuse pattern that is similar to coke. That wouldn't work with mdma wouldn't it? And of course there are many people who never tasted (genuine) mdma and use meph as point of reference for evaluating new drugs.
no, tolerance to mdma increases significantly. the more mdma you do in a short period of time the quicker tolerance builds. out of curiosity to test tolerance i did mdma 3 days in a row. i have a little tolerance b/c typically 200mg of mdma puts me where i need to be, anything less than that is just not quite enough. i try not to redose anymore b/c redosing really builds up tolerance for me, keeping in mind i've been taking mdma for many years. anyway after a month break of mdma, one night i took 600mg mdma, 200mg to start then 2 redoses of 200mg a piece. i rolled very hard for a very long time, i shouldn't have done the 2nd redose b/c it was after the euphoria wore off and just gave me very minimal euphoria with primarily stimulation - it was a waste, my serotoninergic window had already closed. the 2nd night i took 600mg mdma, 200mg to start, then redosed throughout the night, it was a good roll in that euphoria was present but it wasn't as good as the previous night. the 3rd night i took 400mg, 300mg to start then 100mg a little over an hour later. on the 3rd night i felt the need to lay in bed, curl up and nod, however the euphoria was lacking. on the 3rd night my pupils did not dilate and i had a mild appetite that was not suppressed that much. as i said, i was not "rolling" and there was no euphoria, instead there was a strange mental high that was not familiar to me. the jaw clenching and nystagmus was not present and instead, was replaced with what can only be described as restless legs. i've never had those effects before in my life. the batch of mdma was the same for all 3 trials, purity was known - freebase distilled and salt recrystallized, purity at over 99.9% via gc/ms. the following week was like a typical "you did way too much mdma for way too long" type of week, felt overly emotional, derealization, trouble sleeping, typical effects from a lack of serotonin. one thing that was new that week was that the entire week i had a feeling of a threshold dose of LSD. everything was colorful, vibrant, and unique much like a very mild dose of LSD. the problem was that throughout that week it never wore off and caused moments of intense anxiety. i knew it was temporary and rode it out, i was feeling better by a week later, after a couple weeks i was close to back to normal.
so no... you can't abuse mdma in that sense. tolerance builds very rapidly. i've always suspected kids that get addicted to mdma are getting effects from adulterants such as *amphetamine, etc, rather than the mdma due to the fact that mdma builds up too rapid of a tolerance. you lose the effects altogether. having said that, about 10 years ago i used to roll every weekend and kept up that lifestyle for quite some time. but doing binges day after day you would need incredible amounts that would most likely pose CNS problems due to the simple fact that you're taking such high doses of *amphetamines.
i've never taken 4-MMC but i suspect the people who binge on it deplete serotonin and end up binging on the dopaminergic effects since 4-MMC hits those receptors much much harder than mdma, which releases dopamine but it's fairly minimal as it's a more selective releasing agent. or perhaps 4-MMC works are a reuptake, i don't really know that much about 4-MMC to comment, i can only comment on the mdma side of things.