1) The principle of maximizing contact between the neck and body at the pocket is a sound one (no pun intended). That's one of the reasons why a set neck delivers great sustain. I've felt for a long time that an ideal bolt-on neck would be one that used a machined sideways-W pocket (with complementary-machined neck heel), such that the neck would slide into the pocket, and then be bolted in to place. The rationale is that such a joint/pocket would do two things. First, it would increase the total surface area where the neck contacts the body. Second, when the bolts pull the neck down to the body, it would make verical contact along multiple surfaces. Keep in mind that the tightened bolts pull the neck heel towards the back of the pocket, but do diddley to pull it to the sides. So if the only direction you can tighten it directly is downwards, then you want to give it more downwards to be pulled towards, and the articulated joint does that. The downside is that there's some precision machining involved, and you can't just plunk any neck into the pocket.
2) Adding mass to the headstock works...sometimes. The question is whether the mass of the neck and body are a good complement to each other. Adding mass to a neck that is already too heavy, or alternately well-matched to the body won't do very much, while adding somemass to a neck that is maybe a little on the light side can help. A quick and easy test of whether more mass will help your guitar is to stand in a doorway and press the headstock against the door-frame. Not hard enough to bend the neck, but firmly enough for the door-frame to absorb the neck vibrations. If the extra mass contributed by the door frame noticeably improves your sustain, then perhaps more headstock mass (e.g., a Fathead or Fat Finger) can help.