It seems Spiral Power got a huge buff in V0.31. Instead of being stuck in the millions, mine now deals 1.1T of damage. It's still less than a millionth of my Click Power, but it used to be much lower, so big improvement. I don't play the Beach anymore, since I got the CGs. I use the Countryside exclusively, because of the absurdly high Pearl yield. Recently, I've only been leveling up a few girls at a time, in order to properly measure how many Pearls I'm getting from Regional Loyalty. However, with only 5 or 6 girls above level 1, I still have a massively boosted Spiral Power. I assume that taking the time to max everyone out would be an even more massive Spiral power-up. I've been double and triple checking the rate of Loyalty Pearl gain for each Region. I listed the Campus in a previous comment. Once I've confirmed the numbers, I'll post the City and Countryside rates.
Oddly enough, the Spiral does absolutely nothing to the Campus girls now, but is still perfectly effective against your Harem Girls. Not sure why, probably a minor bug.