I think most people agree that the PWR_REGEN_MINERAL is not worth it due to the fact that the minerals you add only delay the regen more, and the inability to use the power during the mineral regen period. I'd like to suggest an alternative to make it more useful.
Buff duration: 500
Effect: Reduces extractor cd by 20/40/60/80/100%
While buff is active, extractor has a cd of 5 ticks -> 4/3/2/1/0.
This lowers the downtime while mining, making it more efficient and allowing you to clear out mineral patches much faster. It also lowers the opportunity cost of having huge mining creeps standing around doing nothing.
This could also theoretically be used on future resources that require an extractor to mine, possibly the new deposits.
Potential option: After looking at some numbers, I think could consider adding a secondary multiplier on the harvested amount while boosted. A powered extractor could return an extra 5-25% minerals, or reduce the cd timer of the mineral when it's empty.
Alternatively: a lower power option is a flat 40% cd reduction with a scaling uptime.
Eg: cd is 200 ticks, duration is 100/200/300/400/500