I'm thinking that more types of wrinklers could be added, maybe not all/any of them actually effect a wrinklers cookie gain, but are possibly just for aesthetic appeal. Personally, I think it could make the gramapocalapse slightly more interesting, if, each time a wrinkler is sent to attack your big cookie, you got the (admittedly minor) excitement of seeing a variant. If this suggestion were to be taken to the extreme, and their were hundreds of varieties for wrinklers, then that might generate some a bit more interest.
Also, if the different types of wrinklers did affect the amount of cookies you got when they were popped, it would add the element of "Do I pop that relatively low worth wrinkler now, in hopes of getting a better variety? Do I leave it as is, not wanting to waste the time it would take for another to spawn?". Note that I don't mean that all the new varieties would be positive. Maybe some new types would be worse than the standard wrinkler.
There's also wrinkler spawn time. If this suggestion were to be implemented, the amount of time that it takes for a wrinkler to spawn might have to be increased, to actually have the "Pop now, or leave it" effect, be worth thinking about. This might mean that wrinklers in general would have to be buffed, but I personally don't really like that idea.
If you think it would be too much work to make new graphics for the multiple new types of wrinklers I am suggesting, you could possibly make so that all the wrinklers still looked the same, but some gave a better/worse cookie gain when popped than others. That might add another luck element to the game that you don't want, but it would be the short and fast way of implementing this idea.
I also am thinking that it might make getting the shiny wrinkler a lot less of a special occurence, so that could definately be a downside to this idea.
Also, a new idea for a golden cookie effect that could exist in the "wrinkler update" would be a wrinkler storm, where your wrinklers were maxed out. This effect would probably have to be pretty rare though.
Thanks for reading!