Just realized that in late game the "Grand Balance" Trophy is impossible to get as even just one Hall of Legends produces more than e.g. 600 Deep Mines can produce. That way "Grand Balance" will NEVER affect Hall of Legends...unless I do a hard reset which I surely won't. So please rethink that trophy! ;)
Prestige does not double the payout at 2nd buy! You just add +1 to a multiplier.
So w/o buying any prestige upgrade it is x1, buying first makes it x2, buying 2nd makes it x3 etc.
So no real double-up on the income!