<<Should following aircraft make small speed adjustments based on TCAS to achieve optimum separations?>>
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. If you have a different final approach speed requirement from "usual" let ATC know in good time so they can accommodate you.