I think it may be worth experimenting with allowing casting while dispersion is active... I doubt we're gonna see any sort of damage increase during it's effect however... if you made a 40% damage increase during dispersion you're effectively allowing SW:P to get a 40% damage increase and consdiering it's about 20% of our current dps that would be a huge increase.
So again, I think at the very least experimenting with letting us cast spells during dispersion is worthwhile... i guess they're worried about it's effect in PvP... maybe it should be 70% damage reduction with the ability to continue casting spells?
It should be possible to have the 40% only affect ticks while the buff is up, even if it's a buff on yourself..
Otherwise make it a 40% increase on direct damage spells(mind flay/blast and SW)
Dispersion should be made into something where you can cast, as said before here.
Dispersion - Instant Cast, 3 min CD.
You disperse into pure Shadow Energy, reducing all damage taken by 50% and the pushback suffered from damaging attacks while casting any spell by 100% for 6 seconds. Every 1 second you gain 2% of your total health and 6% of your total mana. This effect can't be dispelled.