I noticed, that upgrading units with perks can become quite tiresome, when you unlock a new perk and you have to upgrade all the units manually.
I'd suggest a unit list of all your units with quick upgrade buttons and an upgrade all button if you want to just simply upgrade everything, while having the necessary cash.
Of course another thing that could work, would be shift/ctrl modifiers for the purchase button of the perks. Holding shift could buy the perk for all units of the same type, while holding ctrl would buy it for all units that can have it, assuming you do have the cash.
I'd suggest a unit list of all your units with quick upgrade buttons and an upgrade all button if you want to just simply upgrade everything, while having the necessary cash.
Of course another thing that could work, would be shift/ctrl modifiers for the purchase button of the perks. Holding shift could buy the perk for all units of the same type, while holding ctrl would buy it for all units that can have it, assuming you do have the cash.