[CS3] Isometric game: object visibility

[Master_X]

Hi scripters,

I am programming my own isometric game (AS3) with dynamic objects (with own 3d engine, editor etc etc).
Objects use 2d image what will be transformed to the proper perspective.

(klik on image for bigger sample).

To keep it all fast en lightweight i build all objects when entering the area (because when playing flash got enough other things to work on).
I have made a function what checks if objects are hitting the visible area(white lines rectangle).
If a object does not hit the visible area i set the object visibility FALSE else if he hits it is set to TRUE (because its within the visible area.

Now my question is: Are invisible objects use cpu power? (the x and y will always be updated even if the object is invisible).
EDIT: or should it do removeChild and addChild for setting it visible or not? (i guess adding and removing is slower as using visible true or false)
regards,

MasterX