If you look back at some earlier threads, the right hinge pin has a history of vibrating up ... yet, the left hinge pin seemingly stays in place. I have noticed this as well and now place the bent portion of the hinge pin under the shop head of a rivet ... which seems to hold it in place. So there is some sort of a dynamic working on the right side lower hinge.
I'm not noticing the wear you mention ... are you using any type of dry lubricant on your hinges? I've always used the waxy Boelube on all my hinge pins.
Since you are missing the two upper eyelets, you will likely want to replace your hinge. Perhaps you can get by without the need to repaint the fiberglass if you first spray paint the heads of the replacement rivets with matching paint for your cowl and let the paint fully cure for a week or two prior to beginning the hinge replacement. When you are ready to replace the hinge, use an Exacto knife and very carefully scribe around the rivets so when they are removed, you won't chip the surrounding paint. (If the assembly instructions were followed correctly, these rivets should be slightly proud which should make using the Exacto to scribe a little easier). Drill out the old rivets, insert the painted rivets and cover their heads with riveting tape and set the rivets.
Sure, you will be able to see the repair if looking closely, but you may be able to live with the results if done carefully. If you don't like the results, you can always paint the entire cowl.
As for stronger hinge material ... Aircraft Spruce sells stainless hinge material. Not sure if it is in the size you need, but they do sell it.
Happy flying,