If you can demodulate the signals, they're not noise! That technique is called SIC (successive interference cancellation). Basically, you start with the stronge

If you can demodulate the signals, they're not noise! That technique is called SIC (successive interference cancellation). Basically, you start with the strongest one, demodulate it, subtract it from the source signal (which removes it as a noise component), rinse and repeat. Besides that, the benefit of having more satellites available in difficult geometric arrangements (urban canyons, steep valleys etc.) most likely more than makes up for the slightly decreased SNR in situations where you can view "too many" satellites at once, to say nothing of the additional operational redundancy.