It has been generally accepted that you won't stack stamina in Cataclysm. You get most of your health from your gear and enchants without much problem. Using gems that have half avoidance/mastery and some stam is not a bad thing, and even matching a blue socket with a pure stamina gem is not a bad thing.
The problem is that stamina by itself will not increase your time to live. Only avoidance and mastery can effectively do that by keeping the health you already have stable. I believe the argument is that, if you have a lot of health, it only helps if you still have that health later. Otherwise you're struggling to bring that health back. Since the healing strategy and playstyle is such in Cataclysm that your healers can no longer afford to keep you at full health all the time efficiently, you aren't realistically going to have all that extra health you've gained as is.
I'm not saying that having a decent amount of health is not a good thing, nor am I saying that stamina is invaluable. I'm saying that with survival as your key objective, the amount of health you have will not (at this tier anyway) absolutely determine whether or not you survive. What will go towards doing that is your avoidance and mastery, and cooldowns like VB.
Mastery works off of your Death Strike. If your DS is healing you for 25k, and you have 100% mastery, you're sitting there with a shield that will absorb another 25k damage so you don't have to take that damage and reduce your health on the next hit. No matter how much health you have, that will not change the value of your mastery. It is still reducing your next hit. Whether that hit will kill you or not is a different story entirely - for this scenario, we're going to assume that you're not about to die and all you're doing is hitting DS - because the other side this scenario (to me at least) says that you're either setting yourself up to use another CD as it is anyway, or you're not doing something right, or your healer is dead.
ANYWAY. The point I'm making there is that avoidance and mastery save the health you have, making them just slightly more important in terms of your survival. Do I think there is a point where you want to say, I have a good amount of health? Yeah, I just think its easily reachable, whereas survival skills are harder to come by.
As there is a large debate over what to go for in terms of mastery versus avoidance, I would amend your thoughts to simply that avoidance and mastery are at the same basic level (unless you're not very good with your DSs, and you'd tip more towards avoidance... but anyway) in terms of survival. Because: you won't get hit for a huge amount if you're able to avoid some of the attacks, and if you're using DS intelligently you'll mitigate future damage as well as gain back health you lost just recently - again, not taking a huge hit. While I agree with some of what you said, there are some flaws, but I'm sure you see what I'm saying.
As for Vampiric Blood - the reason the glyph is good is because it ties into the healing point I made earlier - healers need more help in Cataclysm than tanks need more effective health. Which is probably part of the reason you don't see its significant impact - you're still caught up in your want of health, versus your survivability. Now, it is true that it will increase the heal of your DS, and leave the Blood Shield alone, but the difference comes from what the glyph does to VB. 40% increase to all healing is much better than the normal 25%. It helps your healers more, and it helps all of your other abilities that heal you, and it does not take that healing away. Note that the increased health you gain is later lost. If your healers suddenly needed to heal you more to bring you up - which they wouldn't be trying to do anyway - and suddenly all the healing they just did to bring your health up is lost, they've effectively drained their mana on nothing. Besides. It has a minute cooldown. You should probably just be using it whenever it is available (or in conjunction with other healing tools like Lichborne).
I won't say anything in terms of the avoidance versus mastery debate other than that you can decide for yourself what you'd rather go after, but also that you should keep an eye out for what happens after this next patch (personally favoring mastery myself)
From what I've said above, I also won't get into your gear and enchants/gems... but I do want to ask about your spec.
First Impressions: you have to interrupt and possibly bring the Abom's Might buff to the raid. From this I would also assume then that you're raiding 10 man content, and further, that your friend is the healer (joking of course, but if he is... well then it's just hilarious).
The third point in Scent of Blood is largely unnecessary, as the gain from it has been pointed out to be minimal at best. The choice of putting points in Blood Caked Blade isn't surprising, but not putting any points into Blood Tap is strange (to me at least) seeing as how you want to have more runes available quickly, rather than having to wait what seems like an unnecessary amount of time otherwise. Crimson Scourge can be interesting and useful if you're the add tank, but because you won't be applying your diseases through "traditional means" most of the time, it will be rare, and also somewhat detrimental to your health to lose out on the extra Death Strike (as of right now anyway). Since I'm certain that you're going to need every point in Virulence, the third point in Epidemic is all I'll point out. That extra time is only necessary if you are desperately in need of having Frost Fever up and Outbreak just isn't cutting it (for some reason).
That being said, as you don't have the Lichborne Spec I can't say that you're missing any important glyphs, except of course for Vampiric Blood. However I would suggest the glyph of Rune Strike over the glyph of Death Strike, seeing as how if you're going for threat, it is superior to the damage increase that the Glyph of DS brings to the table.
Hope all this helps! =D