Thanks for the replies! Some thoughts on those points:
Support: Already have tripod and monopod, but don't use them much. I agree that they're great if you have the time and carrying capacity to devote to them, but as I mentioned I'm sensitive to weight and bulk issues. Moreover, as I mentioned I sometimes do stuff on travel, which further limits the space and time I have to devote to carrying and setting up equipment. I've been learning to brace myself (or even better, the camera) on a steady surface to steady shots when necessary, and I also break out the Gorillapod from time to time. Thanks for the tip though, it's a good one for those who can carry dedicated support equipment!
Macro: I'm indeed intrigued by it, and I'm definitely interested in adding it to the capabilities of my lenses, which is one of the reasons why I'm interested in the 24-70/4 L IS. While FF may be less ideal for Macro due to DoF issues, it's well-compensated by FF's advantages in low light.
Nikon Crop Sensors: Isn't one of the reasons that Nikon has a 1.5 crop factor? FF > 1.3 > 1.5 > 1.6. I would be surprised if Canon actually regularly outshone Nikon with its smaller sensors.
7D II: I'm definitely going to wait. If the 6D has a pricing history like the 5DIII, it should come down pretty well in price by next summer or so. By that time the 24-70/4 might also drop a bit (given the pricing history of other recent lenses), making the upgrade to FF more palatable. Since this is just one hobby among many, I really can't devote too much to it. I also need to upgrade my 2008 Macbook, for example.

Thanks for reminding me of the anticipated 7DII though!
How Shaky: I haven't really bothered to quantify it, but my shots were regularly soft when I used my Sigma 17-70/2.8-4.5 (non-OS version). They instantly got a lot better when I got the 17-55/2.8 IS. Sure the glass might be sharper, but I know that's not the whole story. =) I appreciate the fact that a heavier body (perhaps with a lighter lens) will feel better balanced and more stable, especially when combined with the better ergos of the grip.
Other Lenses: I definitely agree that the world doesn't begin and end with f/4 zooms, and in fact I'm looking to get some fast primes now that they're being released with IS. I've been waiting for reviews on the 35/2 IS, but if I go FF I'll likely turn my eye towards the rumored 50/1.x IS. That said, slower zooms are cheaper than faster ones and still make versatile walk-around lenses, so I'd like to retain options in that arena.
Conclusion: It seems like FF is indeed the best option for the type of shooting I like to do, as I thought it might be. It's just a matter of seeing how much money the upgrade would really cost next year, and what the available options are at that time. If the 6D ends up getting a lot cheaper or the 7D II exhibits significantly less noise than the 7D, that will help inform my decision one way or another. I'll also be waiting on reviews of the 24-70/4 IS.
And despite me calling that the conclusion, feel free to post if you have other thoughts or recommendations.

Thanks for the feedback!