By the way, that method created a new set of polys between the merge/welds.  There is another method to reduce that.  Take your cube (all hail the cube) and select your polys and duplicate and translate as in the beginning.  Make sure you have an edge around the side.  Go to side view and select all  the polys on the back side and back half of the side view (easy enough to do) and delete.  Then symmetrise.  then when you smooth, there will be a few less polys to deal with.