Considering that the original cranks have useful chainring sizes and will work flawlessly with modern 9-speed chain, I would only change out the crankset on one of these bikes if I couldn't find any good pedals with 1/2" threads for my usage. I have always been able to source 1/2"-threaded clipless pedals whenever I put a good Schwinn on the road.
Schwinn's patented 39-52t chainring assembly works for me here with many of my usual freewheels choices, so I enjoy the original crank's creak-free performance, looks and durability, though I usually remove the chainring guard for weight saving and appearance considerations.
I'd like to think that one's perception of these one-piece cranks is perhaps put into better perspective by seeing a carefully assembled bike with original crankset still in place, so take a look and make your decision. Remember also that the adaptors have considerable weight of their own that gets added to the bike. Perhaps someone else can chime in as to whether the adaptors limit the tightening torque that can be applied to the fixed cup during installation.
Note that removing the chainring guard requires five suitably-sized washers to achieve torque on the chainring bolts.
