Replacing the crankset is a bit of a pin because you have a cottered crank and the bottom bracket is french threaded. You can get BBs for the bike but they're not cheap. Velo Orange sells one at $50 but then you will have a nice modern sealed bottom bracket that you will not need to service for a long time. Harris cyclery has inexpensive french threaded BB cups: Action Bottom Bracket Cup Set (French Thread) - Harris Cyclery bicycle shop - West Newton, Massachusetts. They can set you up with a crank and spindle as well. This is worth doing but it will take some work (and some specialized tools).

Swapping out the original wheels for 700c alloy wheels is also worth doing.