Get the book Training and Racing with Power Meter by Coggan and Allen. Read it. If you still want a power meter after that, and you are ready to either buy or build yourself a training plan and follow it, then go ahead and get a PM.

Is there a problem with your drive train you are trying to solve? If there is, is Di2 the solution?

Other than that... if it's just upgradeitis, the best cure for that is to step away from bikeforums and go for a ride. Spend the money on something else that you actually need, or save it for your next bike purchase. Your bike is only 2 year old!