In what sense is something like Fermented Bicycles good design though? I mean, if I flip a Fermentation and a Bicycle in the same game, yeah, I'm probably going to notice the relationship. What makes that fun? You're not putting any sort of skill to the limit seeing something like that.
I'm not sure if the appeal you're referring to is the Timmy sort of joy of getting to exercise such a powerful effect, which I would expect to have diminishing returns, or if you think that finding 2 card combos is an interesting game mechanic (perhaps you either disagree that Fermented Bicycles is obvious or Fermented Bicycles isn't an ideal example, but one you could grab)
Like, subtler combos are what makes things interesting. And the tactics, of which there is a lot.
I think I'm having a bittersweet experience with it because it seems like the lower ages are better designed than the higher ages. I'm not whipping out some sort of golden rule about "win the game" effects, I think they can be good, but just in general the 9's and 10's feel kind of unstable to me.