we dont ride on a river, but ive heard current affects it. but cloudy doesnt affect it at all. our gps reciever is under our dash and the fiber glass is about 1/2"-3/4" thick there, and we still have signal on cloudy days, we have been using it since the summer, and have only lost signal twice and that was on a ridiculously tight turn and at high speed( no it wasnt a power turn, small channel and turning around with a rider) but it found it again after a second, and the rider didnt even notice the change in speed.
but then again, we also ride on a lake. no complaints at all.
any reason your thinking about upgrading? if your paddle wheels works, why change it?