Ok, I've done some investigating today. Results:
I opened up 7 different Wico arcade sticks, and one Command Control stick. The arcade sticks varied in condition from "rusted junk" to NOS. One user pointed out to me that the Wico grommets they had seen were silver, not bronze in color. Of the sticks I opened, only two were silver, one of which was the Command Control stick. The rest were bronze, the same as Ponyboy's. There were no consistent markings stamped into the rubber or elsewhere. All of the grommets were of the same approximate stiffness, except for the ones from Ponyboy, which are noticably softer.
I installed one of Ponyboy's in a stick and compared the feel to one of the arcade sticks that was in good condition. I could definately feel the difference, but the Ponyboy grommet worked fine- the stick just wasn't as stiff. I've actually seen some user comments to the effect that they think the Wico sticks were too stiff, so these grommets may be the answer for them. They're certainly better than an old, used grommet that feels uneven due to the cracks in the rubber. These do feel about as stiff as Wico sticks with a spring in their base, like most of the microswitch based Wico sticks do.
I would say these are a viable fix for a Wico with a torn/cracked grommet, but anybody planning to use them should replace the grommets in every Wico stick on their control panel at the same time if they want a consistent feel from stick to stick. They are not reccomended for players who like a really stiff feel to their Wico, but should be great for anybody who thinks that standard Wico's are too stiff, or prefers the feel of a "broken in" one. They're probably also a good match for anybody with spring-based Wicos.
Hope this helps future shoppers.