I am redoing my basement. My plumber suggest I should change my 3" galvanized steel pipes on my hot water heating system that run across the hole basement for 1" copper pipe. I currently don't have any leaks or any problems. it would just be done so I can gain more height and will give a better finish. Is this practical, or the pipes I have are better then copper he wants to put in place?
Pay now or pay later. Galvanized pipes inevitably fail over time because they crud up from the inside which constricts flow. This reduces the thickness of the wall, so if the flow doesn't get you, the failure of the wall will.
Having said that, 3" is huge, so it would probably take a while before you noticed flow constriction. You'd still have a problem with wall failure.
It sounds like you're putting up a wall finish now, so fixing now would be cheaper, as you wouldn't have the future process of [demo/ re-pipe/ re-finish].
If you knew how old your existing pipe was, you might have a shot at predicting its lifespan.
See also: Galvanized pipe life expectancy