Moved to Roofing and Siding forum.
#1, You need to figure out your wall make up first to see if the added cost is worth it.
Is it 2 X 4's or 6's?
This is strictly my own opinion.
Adding 2" thick insulation on a retrofit Is going to force them to have to build out all the door and window trim a lot so the siding does not stick out past the trim.
Adding fan fold insulation and using insulated siding would add about an R-5, so if you only have 2 X 4 walls that would give you an R-18 wall which is close to the R-19 to meet modern codes.
Do you mean exterior walls? For purposes of discussion an exterior wall has the great outdoors on one side whereas an interior wall has inside living space on both sides.I am not sure what we have behind the interior walls, though the house was built in 1929, I think.