I think AD is, for the most part, untradeable in most leagues. Reason is, as an owner in a few leagues, my asking price is more than I'd be willing to pay if I didn't own him if that makes sense. The response to the owner about Westy, Smith, and Brady is just about right.
The only guy that will make a deal reasonable is using SJax and even then a small bump isn't usually worth it for the AD owner unless he prefers SJax and a larger bump isn't worth it for the SJax owner as the difference between the 2 probably isn't that large.
The way I try to explain it to people that want to trade for AD is imagine what it would cost to get LT back in 2001 if you knew what he would do the last 7 yrs. When you consider that, even Westy, Smith, and Brady is barely enough. Now, I know some of you say there's no way to tell that AD is going to do what LT has done for even 1 yr let alone that many. Well, I believe that he's capable of it and I'd rather be wrong and keep him than be right and trade him away. I know not everyone shares the same opinion about him or his trade value, but that's how I feel about it and I'm quite comfortable with it as an AD owner in a few leagues.
I think your last paragraph nails most people's opinions. While I don't think AD will have the longevity of LT, he should put up some monster years. He's more likely to have 4 of the best years ever produced by a RB than 7 years like LT. Aside from SJax, who else is close? LT/Westbrook? Maybe for a contender, but the age is a key. Addai? Maybe as 1/2 of the package, meaning you'd have to include someone else of comparable value, so Gore + Addai? Not if the AD owner has a legit RB2 already - besides, would anyone actually give that?
The Westbrook, Smith, and Brady package, while apparently excessive, is about what I'd want for him where I have him. In leagues where I don't have him, and I have another QB I like and depth at WR, I might actually do that - if not in contention this year. Problem is, if I have those 3, I'm probably in contention.