So, you have two seemingly similar, but in practice very different kinds of heavy infantry here. First off:

• The Greek hoplite used a shorter spear and held it with one hand. The Macedonian pike was much longer and held in two hands.

• The Macedonian pikes were so long that several rows of pikes could stick out from the phalanx's front, which allowed more spearpoints than targets at any given time.

• Most importantly, unlike the Greek phalanx, the Macedonian phalanx was not designed as the primary decisive force in combat. Instead, the Macedonian phalanx's job was to hold the enemy in place until gaps would form in his line, which then could be exploited by a charge from the Companion Cavalry. The Greeks used the infantry phalanx as the primary decisive unit in combat.

So, given that we know this, we can expect the Greeks and Macedonians to have a different approach to the breaking of a spear. Let's take the Spartans around the time of the Persian Wars. They had servants who accompanied their phalanges into battle, and these servants could run spears up to the front, if necessary, when spears were broken. Or, more likely, the servants would hold spares in reserve, and when a phalanx broke from actual clashing with the enemy (a common occurrence) the spear could be replaced. When a tight clash was on, if a spear broke, the Greek hoplites carried a small sword called a "xiphos" which they used to get in close and stab their enemies at very short range, often targeting the less protected groin.

For the Macedonians, a broken pike was not as much of an issue. First of all, there were a lot more pikes than men in the very front line, so some loss could be dealt with. Second, the job of the Macedonian phalanx wasn't necessarily to kill the enemy directly (although this was nice if it could happen), it was just to hold him in place. This does not require stabbing as much as engagement and pushing in close. This can be accomplished with or without working spears. The Macedonians also had short swords they used when in very close, by the way.

To my knowledge, Macedonians did not "swap out" positions on the line for a broken spear (although it's theoretically possible this could happen). They stepped up to fill gaps when men were wounded or killed, but otherwise, the line remained where it was in order to achieve a continuous push and hold. It's also worth mentioning that the Macedonians traveled with far fewer servants -- only one servant for every ten men -- which made them very quick logistically, but limited in terms of in-battle resupply.

I don't know about more experience, but the typical Macedonian phalanx saw the commanding officer (lochagos) in the front rank of the file he was commanding, with junior officers (or NCOs) in the center and back of the same file to maintain cohesion. So, since the officers were in the front, it's very possible that the more experienced guys were in fact the ones right in the thick of things.