Re: What discourages you on the water?
If I feel any discouragement on the water it is born of my own limitations in knowledge and skill. There is a gadget for just about every task and management challenge in fly fishing but I wouldn't discourage anyone from coming up with a "better" way.
I don't have any ideas for filling any essential need but I have an idea or two for a couple of useful though unnecessary and completely trivial gadgets. The first one would be very cheap to prototype for a project.
1. Indicator Yarn dispenser: Use one of those plastic caps for holding and hanging floatant bottles. Attach 3 or 4 inches of clear plastic tube. Stuff in a length of your favorite yarn mixture in the right diameter and cap off with another soft plastic cap cut/perforated like a starfish. Feed the yarn through like a kleenex dispenser. Probably good for two to three quick indicators on the stream.
2. Stream thermometer strip built in to wading boots and/or waders: More of a feature than a gadget really.