Re: Pedals "Worn Out?" or Something Needs Replaced?
If the foot board is what is moving, check the screw that holds the foot plate in place. If I am correct, your pedal allows for moving the foot board forward or back. If this screw is loose, the foot board will pivot from side to side at this screw. If not the screw, check the hinge where the plate and board connect. These have been known to wear out after time.
If it is more than the foot board moving, start checking screws everywhere. I would start with the spring perch, since you said higher tension helps. If the perch screw is loose, the shaft could be possibly moving side to side between the bearings. Check the cam screw. If it is loose, it can potentially move laterally on the shaft, torquing the chain, thus pulling on the foot board. A loose cam can also have enough play in it to explain those misses you are experiencing.
Without actually seeing it (make a video, hint hint) or getting my hands on it, there is no way to tell for sure what the problem is.
Wanted: GURU 13x7 Segmented English Ash & Ovangkol with Ovangkol Segmented Hoops