I normally build a second townhall so I can double my lumber income. This way I don't have too much gold or lumber (although I actually sometimes get too much lumber and have to make a bunch of Ignited Scourges or begin Ceding my Shades).
I guess lifesteal would work well with their high damage, but would it work on blight too? They can already put up a significant defence due to towers having a multishot magic attack and their units having great regeneration.
What would I like to see? I have one thing that relates to the Lost (not something I want to see, though). Do the other races have a way to get rid of blight easily? I haven't played against a human playing as Lost who used Derelicts to make blight inside my base, but I've done it against the AI. Is there a way to get the blight out?
Redundant units? Well, I'm not one to use spellcasters very much so I'm not really too good a judge of this, but the Incursus is a unit I don't use much at all. It's fragile and dies easily off of blight and the Stygian Monarch always seemed like the better choice since it was so powerful.
Writhing Advocates never really seemed that strong to me, although I liked the fact that they were naval. I never built them until I had an excess of lumber due to the mana regeneration of my Core structure working on both of my town halls, then they became useful.
I never used the summon Corrus or Shambler from the Derelict's Palette, mostly because I liked Nightmares more than Shamblers and Corruses are kind of fragile and not suited to the purpose I use Derelicts for (suprise attacks on the enemy base). I'll be microing my four Derelicts into summoning blight and units that I'm not able to control the Corruses, which have no autocast spells. You shouldn't take those units out of the palette, I'm just voicing my opinion about them.
I do use Corruses sometimes because Predictive Eye is cool, but I use Razors a lot more because they're much much more combat oriented.