I don't think "Griefers will try to blow up the ships" is really that big a concern.
As was said, the Powerplayers could be flying around in giant dreadnought battleships and probably be accompanied by three dozen escorts which would all focus fire anyone that started hostilities. Still feel like 30 NPC defenders wouldn't be enough? Give the battleships a Macross Cannon that can take out an Anaconda in 2 hits and oneshots anything else and it fires every 10 seconds.
Because the more outrageously OP you make the Powerplayer's fleet, the more it puts them over as a legitimate larger than life threat.
In fact...people attacking such a fleet would be a perfect mechanism for Power Collapse:
1) So far all I hear about the idea of powers collapsing is 'if you're in the bottom 3 you have a random chance to collapse.' Maybe there is a more complex mechanism under discussion but from what I've seen my impression is one day there will be a Galnet posting "Ooops, everyone has abandoned Archon Delaine and he doesn't exist anymore."
2) Imagine instead if Collapse was ruled not by random chances and rank, but on the requirement to destroy a Power's Dreadnaught. How possible this is would be dependant on the CC, territory and rank of the Power
2a) Someone like Mahon, on the top of the Powerplay, rarely needs to get his hands dirty, so he sees little need to fly personally to locations, and on the rare occassions he does, he has over a hundred ships keep close watch on his battleship. Archon Delaine on the other hand...as the weakest power, needs to bring his battleship into public action much more often to make up for his weaker institutional strength, and he can't afford to waste good ships on his own defense because of other considerations.
3) So under this regime, Powers trying to collapse another power would need to scout enemy territory, find the ship, report on its location to others and go in with huge 30+ attack group, and they still may all get blown out of the sky and would count themselves lucky if they drop the battleship's hull to 90% before it warps out. But it takes a long time to repair such a ship, so they would look again, scout around and plan another attack. In the meantime, members of that power will warp in to defend their Power's ship, and after many such engagements, if enemy forces managed to destroy the Behemoth, that Power is either totally collapsed, or so diminished they are left with only their headquarters.
4) Corollary idea. You want your Player group to become a power? Well one of the steps is to construct a Behemoth Battleship that acts as your center of power. After all, any minor faction getting too big for its britches could be crushed by a proper Battleship coming in and destroying their fleet....but no Power wants to run the risk of losing their battleship by going toe to toe with another.
It's a thought...probably impossible with the current P2P networking and all the instancing problems, but I like the general theory because it would allow these larger than life ships to exist that are so powerful that to destroy them is essentially a Community Goal. It would add to potential emergent game play and create one vector by which player groups could claim the right to become powers themselves.
