Ashnaile here are a couple of things I would consider for your list:
1) Tyranid Primes NEED a weapon. Even just giving them Dual Boneswords and Scything Talons increases their killy-ness dramatically.
2) The one thing in the list that doesnt really make a whole lot of sense to me is the Podding unit of Dev Gants. 19 guys MIGHT do a bit of damage they drop in, but if they arent near any of your regular synapse they will get freaking hosed. All someone will have to do is 4 wounds and they chances of them breaking are really good. Another thing to consider is you miss out on all the great Synergy of keeping them near the Tervigon. I personally would just double the amount of these guys by giving them flesh borers and remove the pod.
3) As far as your fexes go I would give them twin Linked MC Devs. It's only 10 points more then what you have and it gives them two roles, one which they are retardedly effective in. 24, twin linked str 6 shots per turn is amazing. They are also almost as killy in hand to hand. And to answer "Pil" the reason you attach the Prime to a unit of two Carnifexs is he will be great for wound allocation and making sure they are within Synapse range and do what you want them to. Two Carnies with MC Devs and a Prime is an awesome mini deathstar unit. If you give the prime a deathspitter and dual boneswords with adrenal glands you now have a unit that gets 27 Str 5-6 shots a turn and a model that strikes with 5 Init 6, str 6, insta killing power weapon hits then followed by 10 str 9 MC hits, and since the Carnies are in majority your prime gets wounded as if he is T6 instead of T4 if he is with teh warriors.
I also think that saying if you take a Venomthrope in your army makes you a bad player is a pretty silly thing to say. So far in 5th ed I have won 2 major tournies and always placed in the top half for the ones I havent won and I take a unit of two venomthropes and they ALWAYS are awesome. You should try them out, you might be surprised (key point...target saturation is your friend )