I live in a split/tri-level home that was built in the 50's where from the main level (Kitchen, DR, LR) I walk down six stairs to the Family Room or up six stairs to the bedrooms. My home is mainly brick exterior, however there is siding from the bottom of the windows on the bedroom level on up. The exterior walls in the bedrooms are very cold in the  winter and my AC cannot keep up in the summer. I have having insulation blown into both attics. I am also debating on whether to remove the old siding, wrap the house, and put new siding up or to do all of that and have insulation blown into the wall cavities while the siding is down. Do you think that is overkill or will the wrap be fine. Note, I just had new windows installed in the bedrooms and you can still hear everything that is going on outside.


 My first recommendation is to bring the insulation in your ceiling up to an R-49 and make sure the attic is ventilated properly.
Houses built in that era normally have 1-1//2" R-7 in the exterior walls.  That is assuming the walls are 2x4s.  Today's standard requirement is an R-21 in a 2x6 outside wall.  Your situation is what is commonly referred to as being "between a rock and a hard spot". 
The cost of insulating your walls to their maximum potential far outweighs any savings that you would accomplish.  On the other hand, if you were to go ahead and blow insulation into the wall cavities you would find the house much more comfortable but this is NOT cost efficient.  
Regarding removing the siding and wrapping the exterior prior to installing the new siding is also not cost efficient.  The wrap would provide great resistance to wind, however, no R-value would be increased.  Many companies provide a 1/4" foam-type substance as an insulation barrier before reinstalling the siding.  That 1/4" foam equates to approximately .01 r-value.  In essence it is impossible to bring a house built in the 50's up to today's energy code and requirements for efficiency.
Replacing the windows on the second floor was a step in the right direction.
Bruce Jones
The Insulation Doctor