Speed tolerance, at least for me (and I'm presuming that you are American, and thus by "speed" you are referring to meth...if you are non-American than you mean "amphetamine" I would guess) develops fairly quickly. If I'm only using it once or twice a week, it's not usually a major problem -- yes, I do need more the third day in a row, but not THAT much more.
I haven't noticed any real cross-tolerance between meth/amphetamine and MDMA -- I won't roll quite as well if I've been tweaking recently, but I believe that's more because I've been using up serotonin and dopamine, and not becuase of actual tolerance issues -- thus taking MORE MDMA cause you have been tweaking will NOT help you get more "high" from MDMA.
I would say using meth/amphetamine around twice a month (preferably not too close to rolling) and rolling a couple times a month as well shouldn't be a problem tolerance or quality-of-high -wise. But then, since meth/amphetamine (and esp meth) are pretty neurotoxic, and MDMA probably is too, using these drugs generally isn't very good for you.
------------------
"All the bad boys/are standing in the shadows/And all the good girls/are home with broken hearts."
-Tom Petty, "Free Falling"