If I wanted to say, for instance, C'est bon, la salade, should that be bonne ? Should the adjective match what I'm referring to when I use it that way? It seems very clear that it should, grammatically, and yet I can't recall ever seeing someone say C'est bonne.
C'est bonne is ungrammatical.
Bon must agree with the subject which is the neutral pronoun/deixis ce, so stays in masculine. When used to describe or comment on something, c'est is always followed by a singular masculine adjective:
Des salades aux truffes, c'est bon !
Note that there is agreement with personal pronouns which must agree with the real subject :
Elle est bonne, cette salade !
Tes salades aux truffes, elles sont bonnes !