I think people would be happy enough without the silver and gems; all that gets is jewelry. Plus, if we take out the silver and gems, we open up two wildcard slots, making it easier to get a complete trade circle. Ideally, one of the wildcards would be wheat (best resource in the game), and the other either fish or water (the latter would give beer.) But for just getting a trade circle, I say we drop silver/gems as requirements and just have two wildcard slots.
Besides, +happy doesn't help nearly as much as the +citizens from, e.g., wheat or fish.
(edit: having two wildcards not only makes it easier to get people who fit the circle, but if they turn out to be good wildcards, it'll improve the quality of the circle, and more people will *want* to join.)