Sounds like cheap spokes are the primary problem here. They've reached the "beginning of the end" of their fatigue life.

If it were me, I'd say, "you know what, I ride consistently and enjoy it. I can justify spending a little money on this and really solving this problem" and I'd have a good wheelbuilder hand-build a new wheel with a Mavic CPX33 rim, and probably butted 14-gauge Wheelsmith spokes, alloy nipples and a new mid-level Shimano-brand hub. Then ride it 200 miles, take it in for a fine-tuning, ride it 1000 miles, and take it back to have the tension checked. Between the good spokes and a stiffer rim, that should carry you a long way