You cannot repeat this often enough. The amount of content in Vanilla is not comparable to any other expansion, it's less, just more time consuming and tedious.
I already have a job. I don't mind spending time in achieving things which matter to me. I have maxed out both main professions on all my characters, have maxed out cooking on most of them, and work on fishing currently. I return to old content for leveling or farming transmog, mounts or achievements. I also revisit festival events on at least one character just for fun. But I don't want the little content available to be streched with artificial time sinks. I rather replay the content with another character if I feel that it's not sufficient to fill up my gaming time.
The only things I would wish to get back are the old versions of revamped dungeons at their respective level (so I could farm the ZG tiger which I could not never win when it dropped), or having a TW for the old ZA amani bear (same bad luck on rolls every time we made the time run). I would also possibly like to revisit old Desolace just because it was perfect in capturing the feeling back then. But I also would like to get another chance on MoP CM transmog sets. It's not specifically Vanilla I miss. Because I already did most things I wanted to do in Vanilla, and I want to experience something new.