It would be nice that as well as being able to build higher tiers of conveyors, using gold and then diamonds, if it would also be possible to upgrade from the iron ones to gold ones and then to diamonds ones. Would mean that the ones you make early game are not wasted as you tier up in resources.

Why did I never think about this. I'll do it similar to Iron Chests where you can either craft them to better tiers, or you can use an upgrade and right-click.