If you are coming back to the game after a long break, the new content that has been added during the past seasons is probably enough to keep you entertained without having to purchase VoH.
I played till mid-season without the XpaC and was doing perfectly fine in any game content. Finally purchased it. I have access to the Runes, the Mercs since a bit more than a week and haven’t seen much benefit in terms of performance for my builds.
As a still regular player, I appreciate having a new region to explore and a couple more activities (I play solo and won’t be doing the Citadel).
VoH story is short and I found it quite bad but this is just personal taste. You might like it.
Buying VoH now will also give you the possibility to play maybe the most broken build ever. It will be nerfed next season so it is your only chance.