I own Destiny but neither of the two available DLC are either worth it?
Oh my days definitely not.
The Dark Below is terrible. You can beat the story in an hour, 35 minutes if you're rushing. Crota's End raid is decent fun, but not as good as the Vault of Glass.
House of Wolves has a very very good campaign, but the Prison of Elders is lacklustre. Most of the quality - of - life improvements it made are also in the base game. The Trials of Osiris are excellent to be fair though if PvP is your thing and you've got a strong team.
If you want to get back into Destiny, wait for the Taken King physical edition and just sell on your base game.