Mematine by itself will release dopamine so I suspect some people are not necessarily seeing a reduction of tolerance but rather combined effects of Mematine + whatever. Normally NMDA receptors are excitatory but they have a lot of input to inhibitory interneurons, so when you block NMDA with an antagonist you shut down the downstream inhibitory neurons as well, this results in increased neuronal activation across the board.
Long term potentiation /genetic changes (something called DeltaFosB) probably explains your report of increased tolerance after a break. Long term potentiation basically means that if you keep on stimulating your dopamine every day there are changes that happen in the brain (like dopamine receptor up regulation / sensitization) that make the dopamine stimulation even more powerful, I suspect you lost some long term potentiation when you took your break. When concerta is taken long term it has been shown to improve dopamine flow in the brain.
A lot of long term potentiation is mediated by NMDA so I think it would be wise to avoid it to get the most out of your concerta but you could try memantine, just be aware you might just be getting high off the memantine and it might not actually be a tolerance reduction. Experiments with taking solely memantine would prove wise. NMDA is very important for learning though so if you are studying I would avoid taking it.
Also I wouldn't trust anything you read on these various chemical vendor sites, they are trying to talk up their products.
What I would have you look into is Piracetam, it is a mild stimulant that enhances cognition and focus. It actually boosts NMDA (opposite of Mematine) so it might help potentiate your concerta long term or you might find you don't need your concerta with it. I wouldn't take any racetam regularly though, I would take breaks often. Also get good sleep and take antioxidants like vitamin E regularly! It's a good idea to take anti oxidants with concerta as well.
Just so you know it's pretty hard to always get euphoria from concerta, eventually you build a tolerance at some point. Try to use it for more medicinal purposes haha. But like I said if you need focus you might try experimenting with Racetams like Piracetam/Aniracetam but vary your usage and take breaks.