I've played all the DLC for ME2 and 3, though I cant speak on 1. It's been a long time but I remember all the story DLC being better than most of the in game content. I've never once regretted it, and in some instances it will give you a badass new squadmate. IMO Mass Effect DLC is definitely worth it.
I think Andromeda is worth playing. It has excellent combat and I liked some of the characters. It's pretty cheap now so if you're craving more mass effect when you're done with the trilogy I think it's worth a try.
1. Sounds like most the DLC is well worth the price of admission, much like Dragon Age's. If any of it is near the same level of Dragon Age: Awakening (granted, a stand-alone continuation of Origins and not DLC, but still), count me in.
2. Might give Andromeda a go depending on how I'm feeling after finishing up 3.
Yeah, Citadel is 100% worth the price tag. I paid I think $15 for it and felt totally satisfied with the purchase. Enjoyed it more than a lot of full priced games, and it's got a decent length, think I got about 7 hours out of it, and it's a beautiful and near perfect send-off to the trilogy and the characters.