After 2 weeks of it, the idea was good, but it was targeted too high up. I think the best thing is to keep the "Powers", but relocate any direct powerplay activities down from the power to the minor faction, and use relations with minor factions to drive it. Use the existing minor faction missions to determine minor faction status and action and infer certain powerplay-like actions based on the type of mission done for the minor faction, in the given system, add an "Influence" measure which builds as missions complete. Influence is gained along with reputation, but what missions, and how much adds to the influence depends on the politics of the faction, not the credits:
i.e. an assassination mission may be worth 400,000 cr, which adds to reputation and influence alike, the reputation stays the same, which determines type of missions available, but influence wanes over time, or could even be negative, if it's a mission that the faction doesn't really approve of (but a member issued). This then gives a player dilemma of well, it's a lot of credits, but influence will be negative, so do I really want to.
Influence stays as-is if you haven't logged on for a week, but for every 3 days afterward, drops by 10%. nice, simple, clean, no weirdness, no logarithmic buildup. So it's more a "what have you done for our people this week". Influence then drives cross-system actions, which the player can then choose types based on the current state of the relationship with the neighbouring factions, and this then opens up more powerplay-like "Faction Actions" like Trade Agreement (for specific cargo bonuses), Peace Accord (lasts for a week, reduces security presence in both systems), Police Patrol (lasts a week, increases the bounty on hostile attacks, either faction can come to the aid of the other, police patrols are increased at RESes for example), Joint Operation (assist a famine-gripped system, invade somewhere), until enough of these are done to then get a "Friendly" cross faction relationship, and then at a sufficiently friendly rating, one can merge with the other and/or choose a power alignment, which then provides system-specific bonuses. Players donate their current faction influence during the voting cycle, which then gives votes to choose actions, which then expands the minor faction into the system and the Power goes along for the ride. Likewise, undermine, fortify, control actions all take place in inferred actions based on Missions at the minor faction level, and the sum of all of these actions for all relevant factions applies to the Power.
Vote aren't reset to zero at the end of the cycle, they only reset when an Action takes place, so the player can gradually donate influence over a number of cycles to then trigger an action, or influence can trigger up to 3 actions at a time.
This lets people build stuff up in their "home systems" with friends and groups first. Then use this to drive the powerplay mechanics, which in turn drives the generation of CG's, which don't have any automatic alignment, and keeps pilots as "freelancers", but these CG's are used to expand minor factional influence across to adjacent systems and so on, such that "powerplay" is more personal to the player, as it applies directly to the player's circle of operations, ticks faster with more immediate results, and no need for a decay, plus visible changes (like a change in trade price for certain goods). The influence gained from successful faction-specific missions then drive alignment decisions for the minor faction, which then influences related trade and equipment prices with neighbouring systems. Thus keeping any changes to the game near the player's sphere of play.
Minor factions then choose, on a weekly basis, a Power to align to, and this then provides direct capital into the power based on the size of the combined minor factions aligned to the power, to then determine bigger CG's.
But, pretty please, tier the bar graphs and don't show accurate progress, keep it abstract, keep people uncertain about how far, and they will keep pushing. Carrot, not stick.