replace old galvanized and cast iron that's fine now?

i've got the ceiling open for a remodel in my downstairs bathroom. much of the supply and dvw for the upstairs bathroom is now exposed.
should i replace whatever i can reach of the 1920's galvanized supply and cast iron dvw? it's not leaking at all and appears to be in good shape.

also, the upstairs shower drain is only 1.25". is there any point in replacing the cast iron trap and drain line and making it bigger if i don't also replace the actual shower drain (which i don't want to do because of the vintage hex tile floor)?

thanks

That's a tough call.

Some would say if it ain't broke, don't fix it.

If you've had problems, it may be a good time.
I'm the type that tends to gut bathrooms and redo them every so often.
I'm in a house now that's on it's third kitchen,
The main bath has been gutted twice, now on it's third configeration,
The guest bath with sunken tub has been gutted once, it's second.