this isn't meant for a a single player, the size of a ship required to preform such actions would be by it self an impressive achievement, requiring the input of (purely speculative) say 100 players, and operating it would require as many again, its an idea to solve a problem that wont appear and present it self for a long time, which isn't to say people wont strive for larger-scale operations on their own terms. EVE shows this very well.
as for power and efficiency, this wouldn't be simple efficiency in terms of greater output, eventually a level is reached where it becomes the next step, by this i mean, mining with players and ships will reach a point where a bigger ship has capabilities the smaller ships cannot achieve. Another EVE example is the Rorqual.
It is rather funny you should mention EVE, im a veteran of 8 years, and organizing a fleet to mine entire belts was my thing, so i can say i wouldn't get tired of devouring a planet
i will admit, i strive for complexity and advancement, even crave it, and it being a game is exactly why i would like to see it, i realize my idea is not a short term, rather a long term or far future idea, if it should ever reach such scale at all.
Now. as for everything being a potential weapon, it is true, it could be, but as with anything, it is how it is used.
Examples of your argument are the likes of nuclear weapons and nuclear power generation, it is entirely up to the user.