As far as does it matter, galvanized will rust internally, and narrow the size of the pipes all the way down to nothing, which will obviously affect water flow considerably.
think of an artery in your body getting clogged. old galvanizes pipes rust internally over time. they used galvanized in ww2 era because copper was needed for war. but now we have old galvanized lines that are clogged.
Start with checking pressure at faucets by adding gauges. could be the faucet cartrige themselves are old and clogged before the aerator/showerhead. i would try disconnecting the flexy under the sink and run the water into a bucket or on a gauge to see what the pressure is before it gets to the faucet. Also, is it hot or cold having the issue? check your hot water tank.
it doesnt sound like a pressure issue- sounds like a volume issue.
