M777A1 vs M777A2 Excalibur

[Imp]

Boosting experience by any degree would effect many things, issues with arty I can think of quickly.
Increased rate of fire so an extra shot.
Becomes far more effective at counter battery fire, this is based on experience a low experience unit will rarely do so.
I cannot remember but I think it is the experience of the spotter if it has eyes on target that determines how accurate the fire is along with mods for GPS etc.
The experience of the arty crew has a minor effect on the kill pen if I remember not the "scatter"

The only real fix would probably be a whole new class with tighter scatter routines, only really have any effect if you did not have eyes on target however as grouping is normally pretty good already if target hex is in LOS.