Yes, Sweet as an (almost) antonym of Salt, and as a adjective describing Bournville Chocolate makes for a double reference, similarly to Ada relating to both Ada Lovelace (and Mrs Gillyflower's "baby" Analytical Machine) and Ada Salt.
I think they made a deliberate effort to go all out on this episode, so lots of clever allusions, Diana Rigg, and the triplet of Vastra, Jenny and Strax, all of which were likely to make for a good episode, since it was apparently the one hundredth episode of the revived Doctor Who series.
I wonder what else we've missed, that may yet become apparent?