Currently, beyond level 10, upgrading Chronoforging is pointless, as the benefits become increasingly smaller while the costs skyrocket. A good incentive to continue leveling up would be if Chronoforging, starting at a certain level (such as level 6-7), not only reduced construction time but also began reducing unit training time in both the Barracks and the Warship.
Example: The same reductions used for building time could be applied, using the same percentages, but instead of starting at level 1, these reduction percentages would begin at level 7. This would make it very attractive to upgrade Chronoforging to high levels to obtain these bonus reductions in troop and fleet training times. This achieves the same reduction as with buildings, but seven levels later. This building would become key, it would add a lot of gameplay, it would level the playing field more and make banks more dispensable.