One could say The Buried Age
follows up on elements of "The Battle" and "Encounter at Farpoint," though more accurately it precedes them.
The Jarada from "The Big Goodbye" were followed up intriguingly in Imbalance
by V.E. Mitchell, and to a lesser (and incompatible?) extent in Demons of Air and Darkness
The parasites from "Conspiracy" are followed up in the DS9 Relaunch.
There was a sequel to "The Child" called "Prodigal Son" in Strange New Worlds IV
Klag from "A Matter of Honor" is the lead character in the Gorkon
The Iconians from "Contagion" were followed up in the Gateways
Kyle Riker from "The Icarus Factor" was in A Time to Love/A Time to Hate
And there are various followups in SCE, but you sort of covered that.