Are any of these worth it? I kinda feel that Mars War Log base price is too high. $2.50 may be the right price for me.
Warden's Keep - essential bank. I also really enjoyed the story of this DLC. IIRC, this DLC also gives you the Blood Magic Skill Tree.
Shale turned out to be one of my most favorite characters in the game. - Stone Prisoner
Witch Hunt - I felt as thought they complete broke the story line, just to shoehorn that in. No, you don't get to have sex again with Morrigan.
I don't remember anything special about Leliana's song, other than it was super short. ..but it did bring a lot of depth and back-story lore in. I enjoyed it. No, you don't get to have sex again with Leliana.
Both Warden's Keep and Return to Ostagar were pretty forgettable. I didn't play the DS Chronicles or Golems DLCs. It's hard for me to evaluate The Stone Prisoner as a DLC because it came free with new copies of the game when it was released, but Shale is an interesting character. I liked Witch Hunt because it was more Morrigan and I really liked her as a character (and yes, in one of my DA:O playthroughs, I did romance her). Leliana's Song was far-and-away the best of any of the DLCs I played for DA:O, though (and she's a pretty great character too). If what I've read about Inquisition is correct, it looks like both of them will be returning in the third game, but only Leliana as a party member.
One of the several things I didn't like about DA2 was the fact that it felt so wholly disconnected from DA:O because only a few familiar faces popped up. Not only did it not play like a DA game, the narrative unfolded in such as way that it could have been set in almost any other generic epic fantasy setting.
Regarding your list, yeah, pretty much everything there will turn up in a bundle eventually. I haven't played any of them, but Space Run is only 50% off, Contrast and Of Orcs and Men have been on sale for this price before and will be again, and Mars: War Logs has been bundled before in a CAG bundle. I don't think I've seen it cheaper outside of that bundle, but you might be able to get a cheap key from the Steam trading thread. Those three games have fair to middling reviews across the spectrum, so if you're not going to play them soon, I'd wait.
Of Orcs and Men is kind of compelling as a really cheesy B-tier game set in a Lord of the Rings sort of universe, but I'm not sure if I'd recommend it for more than $5 since outside of the dubious dialogue there are a lot of frustrating things about it. I still always feel compelled to go back and maybe one day finish it though, so clearly it did enough right to make me want to see more of it. That's the only one I've played off the list.
This is pretty much what I've read about it, but it's been sitting on my sad wishlist for a long time. I wouldn't buy it at $7.50 either under normal circumstances but I doubt it's ever going to get cheaper than 75% off until it gets bundled, and I have some Steam birthday credit, so. . . .