The only issue I'd see with more expensive triggers, receivers, optics, and lights is that if the rifle is going to be a hard-use ar15/carbine, in the same vein of an AK-47. I don't see a lot of value added on your end by running more expensive accessories/components into the ground when on their best day, they are no more reliable and durable than something that costs 1/4 the price and is still relatively pricey (IE aimpoint M4 vs S&B short dot.)