I do not have a calculation for Divine Aegis on absorbs. Also please consider that the glyph heal is 20% of your total absorbed amount, Divine Aegis is for 30% of the amount healed. (nonetheless it is an important part of your kit, just so that I can be sure, we are on the same page :)
I didn't mean crit is bad for a discipline priest, it is a very significant talent. I do think that still, if you change the legs, you are swapping out many other useful stats too. I did some item comparison, which you can see here, and which I will be using as one of the bases for my arguement.
I only included items from the T10 sets, as the other items can be the same for every gear. For the same reason I didn't include enchants, but I did include gems, as the number of the slots varies and plays an important role in maximizing your stats.
Let's see the 3 builds then:
1. swapping out the gloves as an off set item
2. swapping out the legs as an off set item for the t10 DPS legs
3. swapping out the legs as an off set item for the ICC 10hc VDW legs
If we take your statement as a base, to maximize crit with the given items, the T10 shadow legs would be the best.
Now with this these are the stat differences (comparing 1 and 2):
crit: +122
spirit: -122
haste: -114
sp: -13
hit: +106
As you see, you do gain a significant amount of crit, but at the cost of many other stats. Although it is nice to have extra crit, but not at this cost. You still need spirit for the longevity and haste is not a useless stat either for a disc. These outclass the gain of crit and hit (which you don't need as a healer) by far, thus the legs are not worth to be swapped out for anything.
Me myself like to rely on the certain gain of the flat stats, than the chance of critting more on my heals (let it be the glyph, or anything else).
You can swap around other pieces of gears freely, with which I might update the guide sometime in the future, but the legs are set in stone the best you can get from this expansion.
Although you are free to build your priest as you like, I will not include these legs into the bis list of the guide.