Hi, I am purchasing a property in Nova Scotia, (Hot Summers, Cold
Winters). The property is approx. 60 years old and has had some
upgrades done over the past number of years. However, one thing that
has never been done to the house was the addition of new windows.

Lets see..60 YO home..Hmm

Figure the windows & doors might add up to 10% of the square footage of all
the exterior walls.
That leaves the 90 % which is exterior walls. Then there is the attic
insulation (or lack of)..

I'd do a lot more thinking on how to reinsulate the 90% to try and get
somewhere near an acceptable (by todays standards) package before I'd spend
a lot of time (and money) worrying about 'cosmetic' fixes [since there
are already TWO 'layers' of windows right now]

It may be that the attic has been re-insulated to R40 ..MAYBE the walls have
been done also..I hope so or there's a lot more to worry about than
windows..