I just posted on your other thread. While there is cross tolerance, 30mg is at a therapeutic dosage level. I doubt that it would downplay your MDMA experience that much. Just go a few days without as others have suggested before you take any MDMA.
Edit: unless you are RX'd your dexamphetamine you should refrain from taking it EVERYDAY. This is how habits are formed. Habits lead to addiction, which eventually leads you on a long road to nowhere.
Be safe.