1)Lower cooling performance from the unit during heavier loads.
2)No, if you care at all about the above. Plus there's the cost of doing so...
Few RGB fans match the performance of the Aer P 120s the Kraken X72 comes with, and they're not cheap:
Corsair LL120 RGB - it has to be the 2200rpm version.
Fractal Design Prisma AL-12