replacing galvanized/cast iron DVW piping... recommended?

First of what will probably be many posts as this DIY newbie get his mugs dirty... thanks in advance for your help!

Basement ripped open to studs on 1953 2-story house in Seattle, plan to replace galvanized supply lines with PEX but didn't know if it is worthwhile to replace the galvanized drain and vent pipes??

No leaks known of but just dug up a floor drain suspected of having a collapsed p-trap.

How does one make this decision? Not worried about a couple hundred dollars in pipe cost if it's worth it, but also don't need to mess with something if there isn't any long-term benefit. Be glad to supply a photo or two if that helps shed some light...

CI can last a century, galvanized from 1953 could be worn out, or still fine - depends on where in the system it is. If it is a vent, it might still be fine. If it is a drain line, it could be all plugged up with rust. You'd need to be on-site to determine which.

Keep in mind that CI damps noises much better than the plastic replacements of pvc or abs, so that is an issue as well. CI costs more than the plastic, but if you go with the hubless version, you won't need to learn how to lead a joint.