Vanilla - Nerfarion and Ragneros lots of old god related content there, Cthun was added and thats more old gods related. So Vanilla was pretty good in old god content it had a mix of lich king and other threats too.
TBC - All legion related stuff along with ZA related to the blood elves. An old god does appear in some fashion as its being summoned in a quest chain. (only nod to old gods are Naga but these guys are loyal to illidan afaik)
Wrath - Lots of old god content here Old kingdom and grizzly hills being major areas for it. Then storm peaks and ulduar/5man wings.
Cata - old gods galore
MOP - Old gods galore again.
It is time we went away from old gods for a while give it a rest and lets get on with some legion related shizzle.