Straight up, if you played vanilla Destiny primarily for the SP and didn't think it was worth $60, you absolutely will not think TTK's SP stuff is worth $40. Save yourself the trouble and skip it.
Or do what Deku said, and visit the Destiny OT where you'll almost certainly find a group that can show you around that the game really is. I'd actually prefer you take this route; it's a wonderful game played in a group, and the DGAF people are super nice and helpful.
It's the first game I willingly subjected myself to playing in a party with voice chat with people I didn't know in real life, and it's been great. I've played with MANY of the DGAF folks, and almost everyone has been a treat to play with. In fact, it went from me randomly joining pick-up groups to have a regular raid group made up of the same guys every week. Now we've been playing Destiny and other games (Rocket League) every week for about half a year now.