Trying to find a balance, your thoughts appreciated.

So I'm still waffling as to how I think my gear should go. I'm a non-raider thanks to being a new father and mostly just instance with guildmates. I see most people say +spell damage for 5-mans, but I'm still a ways from 485 def (non-raider) and what not so I'm unsure where to draw the line. My gut feeling is that I should be mostly sticking with the pure tanking items, especially now that I've finally gotten KoT revered sword and pants. I figure the Sword should give me enough +spell to keep me comfortable for the most part, with my BP helping too.

I know I need to upgrade several slots to be really comfortable. Some things, like my current belt and ring, don't appear on the gear lists floating around, so I'm not sure how they measure up to other, easier-to-get items.
BELT:
Despite several tries, I've yet to have a successful Mech or Bot run (can't get past Nethermancer and Warp Splinter, respectively. Wipes us every time) so no belt yet. This may take a while, but I dunno what else to change to in the interim.
NECK:
I'm 1.5k rep from Revered with CE and I'll get the necklace from there. Just found this neck the other day on the AH which isn't bad.
HEAD:
If I can ever get a primal nether I'll make myself a Helm of the Stalwart Defender. I have a Helm of the Myrmidon in the bank that I could gem up (Tenacious Earthstorm and a Solid Star), if that's worth doing. I could also make myself a Felsteel helm, but is it really an upgrade from the X-52? Regardless, as soon as I do I'm sure I'll have the nether drop.
SHOULDER:
Righteous shoulders would be nice, and we did manage to kill Laj before, but I don't feel too badly about these, although I have had them quite a while.
WRIST:
I have Jr. Technician's bracers and a Thadel's that I alternate between tanking/soloing. I also have a Sha'tari Wrought Armguards in the bank, are they really worth upgrading to? I see a lot of people wearing them. I've been looking for months for someone who can make Green Fortress Bracers with no luck.
TRINKET
I'm a 5 and a 7 away from a furies deck, but I don't know whether it should replace the Commander's Badge or the Frostwolf Rank 6. I keep a Regal Protectorate in my bags too for boss fights. No luck on an Adamantite Figurine and I haven't been able to get a group arranged for Dabiri's Enigma yet, and, again, not sure what should replace what when I do.
RING:
I haven't had any luck with a replacement for the Veterans Band, which can't be all that bad, can it?
SHIELD:
At this point with my defensive stats, I don't see a reason to switch away from my Shield of the Wayward Footman; I use my Netherwing Defender's Shield for my healing set.
HANDS, LEGS, BP, FEET, BACK:
Not worried about 'em, comfortable with what I have.

I guess what I'm asking for is help with my priorities, both with spell vs def and what should be upgraded/chased after first. Also, of course, please feel free to point out something obvious that I'm missing. Thanks in advance.
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Armory link FTW?
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Zen Tanking - http://zentanking.blogspot.com

Apologies, I thought it was part of my sig, but even the pic isn't loading up now. http://armory.worldofwarcraft.com/character-sheet.xml?r=Undermine&n=Vanalyn
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Thank you, Guillex, that's exactly the kind of reply I had hoped for. I forgot to mention that I'm Scryer, so unfortunately the belt you mentioned isn't an option.

I've gone ahead and gemmed up the Myrmidon's Helm. I might just pop over to Sporeggar and pick up the Shield there for the seemingly interminable list of daily quests (which is all I have time for lately) and place a shield spike on it for good measure.

Anyone else mind weighing in? Any strong feelings on an instance/drop I should shoot for first?

Our local uberguild just put up plans for Red Havoc Boots on the AH for 1500g. It's painful to look at and not buy, but I can't rationalize paying more than 1000, tops (or am I crazy to pass it up?). I sent them an email to that effect. Of course, then again I'd need 3 primal nethers to gear up ><
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You can go for the Sha'tari Vindicator's Waistguard instead.
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"The greatest trick the devil ever pulled was convincing the world he did not exist."
-Verbal Kint

The top sticky on this forum section, authored by Dreamcrusher, has all the information you're looking for. It's a breakdown of each armor slot and the options available through 5-man drops, quests and crafts, and how/where to get them. The one's with a >5< next to them are ones you really want to look at, as they're best suited for 5-man content with emphasis on spell damage (for threat) and block value (for great mitigative effect. 5-man mobs hit for less than raid mobs, so block value cuts their attacks down a lot, having a larger proportional effect than armor with increasing block values).
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I am the shield that guards the realms of men.