Extra pierce for the shuriken attacks are quite useful for early-game, especially in combination with Seeking Shuriken. It has little improvement for Upper Path 2 or Upper Path 3, as it only affects the shuriken attack, however.
Using a Ninja Monkey with Sharp Shurikens can be used for early game because of its high pierce, fast attack speed, low cost, and camo popping power.
Crosspathing this upgrade with Upper Path 3 is near worthless, as the Sharp Shurikens upgrade only affects the shuriken itself.
As for crosspathing with Shinobi Tactics, it's generally unnecessary to buy this upgrade, as the extended buff range from Ninja Discipline is sufficient. But if adding in Sharp Shurikens can be helpful if a majority of the DPS in the game comes from spamming Shinobi Tactics.