Currently there is no reason to take Minion Dematerializer over Magical Footwear and Future's market. The % damage increase is not significant enough to out weight free boots at 10 minutes that are gold efficient.
Each Dematerializer used shouldn't have diminishing values if used on the same time. Currently, the first proc on one minion type increases damage by 4% and procs after only increase damage output by 1%.
Keep each proc consecutive and consistent in terms of damage out put. Lower the % to 3 but all procs after remain at 3%.
This would be a helpful start, increasing the number of dematerializers doesn't seem to be the right course of action (currently start with 6) because they already take up a much needed item slot.