Well here's an interesting thought which struck me last night while stripping paint off some models (notably a couple of shamen).
With the extra mushroom dice, it's less important for night goblin shamen to have +4 to cast, and they're at a (slightly) greater risk than they were before. So I was thinking "how am I going to protect my great shaman if he wants to cast 2 or 3 small spells (with the help of mushrooms) per turn?".
The answer I came up with was to not take a great shaman at all. For the price of a level 4 great shaman with a sprinkle of magic items, you could get 4 level 1 night gobbo shamen. so what benefits and draw backs does this have?
Drawbacks: no +4 to cast/dispel. Lower chance of getting the spell(s) you want (no rolling doubles, so no choosing spells). No magic items (if you're staying strictly to the same points value as the great shaman).
Benefits: 4 seperate shamen in 4 seperate units = you'll (almost) certainly have something to do in the magic phase, one failed animosity test won't take your whole magic phase with it. Greater chance of channelling. It'll take a lot more effort for the opponent to get rid of your magic (dwellers etc can't just delete your magic in one turn). Miscasts hardly mean anything (oh well, there goes one shaman, only 3 left now....). There's much less risk if you want to throw out the curse of the bad moon at full power, just 6 dice it (plus mushroom!) and if you miscast, it's only a cheap shaman (and probably a few gobbos) who's gonna suffer. Cheap throwaway characters are great sacrificial guys for re-directing charges etc in a last ditch attempt to save an expensive unit.
There's probably a few more benefits and drawbacks I haven't thought of, but this is certainly how I'll be playing for a little while at least (until I realise it doesn't work for whatever reason). Obviously this doesn't work if you wanna use orcs, though I haven't looked at the price of orc shamen etc, so maybe you can do much the same thing there too (though without mushrooms)?
Obviously this could also work with a cannon magnet....sorry, I mean arachnarok with shaman and shrine, but having a big uber shaman defeats the point of the whole tactic really.