I'm not a fan of foot slogging overall as wave serpents seem to give so much more bang for buck.
I'd be tempted to have squads of 5 in serpents.
IIRC wraithguard are 30-35pts each? dropping 2 from the d-scythes and the wraithcannon squads will save about 210pts - add that to the 180 left and that'd be enough room for 2-3 wave serpents and would deal with the main problem of this list as I see it.
lack of speed - even with the voice of twilight, you're still foot slogging for a couple of turns before you're in range.
anything st6 ap3 (heldrakes I'm looking at you!)+ will result in losing too many wraiths to be very effective.
I do however like the wraithblades - a 4++ goes a long way.
Have you considered wraithknights or wraithlords? purely for the long ranged firepower.
At the moment, you've got no guns with a range bigger than 12" - I know spiders are fast so this helps, but you'll still struggle to close with the enemy fast enough and spiders can't do everything