Definitely not. The controller is the only one who knows what spacing is required for many reasons so just follow his instructions. If you make your own adjustments by slowing down it might have serious effects on the one behind if the controller is providing wake turbulence separation.
The controller may know what spacing is required, but unfortunately they are not always capable of providing it. I've lost count now of the number of times I've been told to maintain 180kts on approach when it's quite obvious form the TCAS that we are at the minimum 5 mile separation from the preceeding heavy and he has already slowed down more than us. Of course as soon as we change to tower, the first thing they say is "caution wake turbulence" for being too close. So now I just slow down when I need to to maintain the required separation, if it messes up their flow well that's their fault for not separating us properly in the first place.