I've got a few more games with the bugs under the belt, and have tweaked the builds a little. I'm still forming opinions on some units, and I figured I'd share my thoughts.
I have to apologize for the lower number of posts in March; admittedly that's because I spent about a week down with allergies + sinus infection, and the antbiotics pretty much floored me for about a week.
Hive Guard: I LIKE GUNS!
Ok, honestly, I have to recommend the Hive Guard. This might be a bit of a no-brainer, but these guys are a solid army-enhancing support unit for just about any 'nid army. S8, BS4, 24 inches, and no need for LOS means they're easy to use and can sort out most light armor.
Note that their range is only 24 inches, so against longer-ranged armies you will have to move up to engage them. Then again, if you know the enemy isn't going to come to you, you can deploy forward enough to try to get to them, and unless it's a fast, mobile army you can probably bring them to bear. I know that when I go back to guys with REGULAR guns, it's going to mess me up.
Note also that in a pinch, T6 with a 4+ save can stop-gap a good number of troops if it really does come to that. I had to throw them into assault once in my recent game against double-raider Templar, and it's really hard for stuff like regular space marines to wound 'em with S4. Obviously, this doesn't apply against hard-core melee troops with access to poison or higher strength. It's not something you WANT to do, but it's worth keeping in mind that you CAN sacrifice shooting to hold up lesser troops.
Bottom line: unless you're going for an aggressive posture with drop-podding Zoanthropes (or taking Zoeys with Onslaught-packing Tervigons) then you can probably make use of Hive Guard in your army more often than not. I own 9 now.
Spore Mines: I'm in your DZ, fouling up your deployment...kind of
I've used spore mines a few times now, and the jury is still out. As far as I can see, the major appeal of spore mines is to try to foul up the other guy's deployment. If you want to do this, I would suggest taking three units of three. Past that, it's a matter of making an educated guess about your opponent's deployment, and then chucking spore mines in those locations and hoping they land in a manner that hampers the enemy drop zone.
Once they're down, you can't rely on the mines to do any damage. They move 1d6 in a random direction, and detonate if they end any movement phase within two inches of the enemy. It's an S4, AP4 large blast. It might occasionally draw fire IF it gets close to something. Worst-case scenario, it will let troops that can shrug off the blast assault it and get a consolidate move off it, or something like that.
Bottom line: if you aren't using your fast attack slots and have 60-90 points to spare, you might be able to futz with enemy deployment. Obviously, if the enemy has drop pods or something like that, well, you might not DO that much...
Trygons: ...that's a pretty big mole to whack
I've used triple-trygons once, and it was in a Battle Missions game where only fast attack could start on the table. My initial thoughts with Trygons was to play reactively; see where the enemy deploys and then slap them down accordingly. I got my reserves in first, and Chaos had a Defiler and most of the rest of the army were fellows in Rhinos, along with obligatory Obliterators.
I picked up two lessons from that game:
1) Have a backup plan for Trygons other than 'react to the other guy', like 'slap them on an objective' and dare the other guy to come play
2) Six wounds at T6 with a 3+ is REASONABLY durable, but things like Oblits, that can deep-strike accurately and peg you with twin-linked plasma guns....yeah. You're a melta magnet, hence you bring multiples
You'll bring tyrannofexes only in shooty armies, and you'll bring 2-3 of them. They have a 48-inch reach, which means it's difficult to out-range them. They have an S10 gun, which means they're pretty good for nailing light armor, and can in a pinch threaten heavy armor. Note that even though you ARE S10, you'll still need a decent amount of fire to down land raiders. I would take them with units of Hive Guard, just to get good weapons coverage and to make sure you can halt any lighter armor swarm in its tracks.
Note that like trygons, these guys dictate your army. You will want to screen them, but in a pinch the cluster spines and thorax swarm CAN do some damage to larger numbers of lighter troops. This is a stop-gap measure, but it's good to bear in mind. If you do deal with Land Raiders and the like, still be prepared to punch them out.
Tyranids and Heavy Armor
Admittedly, I have yet to test Zoanthropes. I've still got to kit-bash them together and all that jazz. I like the Hive Guard model, but I have some plans for kit-bashing some reasonable Zoanthropes together out of Trygon bits.
Frankly, I have to conclude that 'nids have three options for killing heavy armor:
1) Shoot it with Zoanthropes
2) Shoot it a lot with Tyrannofexes
3) Punch it repeatedly with monstrous creatures
Against Land Raiders, 'immobilized' is a very tolerable result, as it prevents them from getting closer. Generally, you want this BEFORE the enemy gets close.
The worst nightmare for 'nids would have to be a later-game objective-contesting move from a Land Raider. You have GOT to take it out, and all the MCs other than the Carnifex have around S6, so you have GOT to devote them to assaulting it, and may not nail it first time around.
Hive Guard have a place in just about any army; every 'nid player should have at least a half-dozen.
If you aren't running any fast attack, 90 points in spore mines can provide a chance to disrupt enemy deployment against most builds.
Trygons are nasty, but not invulnerable, and you need a backup plan in case your enemy doesn't deploy normally.
Tyrannofexes are legitimate long-range threats with a nasty point-defense system, though they are army-warping units.
More to come as I get more games in with the bugs.