From what I'm seeing at the moment, secondaries don't. It's a scaling issue mainly, because AP always provides the same amount (an increase of X to your dps, non-scaling). Secondaries however, are (spec permitting), get better with gear. a 1% crit increase (again, spec permitting) at 10k dps is 100 dps (1% crit is 1% uptime on 100% more damage, so 1% more damage overall). if the AP from the itemisation is worth less than 100 dps (possible), it becomes better to favour crit.
Attack power never really stops being good, it's more that the secondaries scale up, being multiplicative bonuses. Part of my original math was trying to work out if socket bonuses were worth it or not, and it kinda spiraled out of control from there (I have like...2 spreadsheets with craploads of formula in them). We're not quite a the level of attack power where secondary stats start to get silly-valuable (unholy dks and tanks in dps gear can reach this threshold, but nobody else can currently, and it's a very small gain even for those). Switching gems to all secondaries also fucks up the whole scaling, as when you swap, the primary stats instantly become more valuable again. The available itemlevel just isn't there. Perhaps if 80s were in 330/340 gear we'd reach it, but not in 277/300 gear. It's enough to push the balance towards sockets (14 str 10 haste being more valuable than 20 str for example, and this applies across the board)
Currently, I'm ignoring all defensive/regen-type mechanics. level 80s don't usually have regen problems, so that puts max mana and stuff at the side. Similarly, dodge or parry aren't useful in a PvE setting (which is mainly how I'm working), so they can be basically ignored.
As for crit from agi/int...well that's a little tricky. It does buff the strength of the stats, but from what I've seen only really affects the specs that love crit. It's a small dps increase that favors crit-y specs over others. But as we've already seen in this thread, some just have waaaay high crit already (I have made a subtlety chardev with 92.5% crit without procs), and secondaries (besides avoidances) don't diminish at all.
I'll get the math up over the weekend hopefully, I've got some time off to sit down and fix the last few things. Expect there to be a whole new thread detailing how the stats scale, and if I have time I'll add spec specific parts too, so you know where to look if you're confused about gemming.
As for the haste vs AP thing, unfortunately you can't exactly weight it quite the same (at least from these talents). Given that you didn't apply any of your math to the original 154.2 AP, it's more important to choose the unmodified figures, so we can see it more easily. In this case, the AP talent is just that bit stronger, at least for MM.
