Cheers for the input guys.
You do have a point about the attrition. Though I believe the chars can't give their WS to the units any more. Even so casting their regrowth equivalent will be a pain.
I was just trying to thing of something I haven't used yet and that it really. The biggest pain now is that when the general dies the army crumbles for a turn then the next guy with a wizard level takes over and they stop. Very annoying when you aim to assassinate. In the tournement game I had he moved his general on the second turn to cast a spell at my eagle which brought him just between 2 units. He got hard cover but a hail of doom and 20 glade guard arrows later and his army was crumbling away. Not going to be as easy.
My main combat unit in that army was 6 treekin that chewed through 40 ghouls and 5 black knights. Now he takes a banner of flame on his ghouls...
I might scrap the idea for a drycha list. Just throw hoards of dryads at the ghouls, treekin and a treeman at the grave guard. Should be fun at the very least bringing units in randomly from woods

A thing to note with the Eternals is they would be boosted by Life magic. Last game he took 2 lvl 1's and a lvl 2 so my lvl 4 should have the advantage on casting and dispelling.
Quick list idea:
Spellweaver lvl4 rhymers
BSB silvered steel, dragon bane
10 dryads
9 dryads
38 Eternals FC razorbanner
20 Glade guard Flame banner musician
2 eagles