Semi Permanent would be nice, perhaps something like "effect fades over time and doomspike absorbs to do additional damage". Having it cost significantly more sense you won't have to Whack-A-Buff as it was so interestingly put earlier. They could still be stacked for the same increased cost slowing the rate of decay from say 100% decay @3mins. +1 min/stacking so up to 5mins. Once you've reached III the cost could be reduced to a "upkeep" amnt rather than the full buff cost.
And just get rid of dreadspike it's garbage, Drain Samba ok, Haste Samba GOD YES ... Wait this isn't dnc