Might want to call a couple of plumbers and see if they can fix the problem
first before going to all this work. Sometimes valves can be replaced and
improve things a bit.

yeah patch sounds good till the pipes rust thru, creating leaks or a
flood.

this happened to a buddy of mine who refused to replace the lines,
leaks everywhere he finally gave in and replaced all the galavanized.

do note flat runs are more likely to crud up, but sooner or later it
all will have to be replaced