Not a considerable amount

You're about twice as tall as before - large enough to stomp small houses with a single step. Seems there are some diminishing gains to this.

Feels like your growth is messing your thoughts up somehow; with size comes distance, and with physical distance comes emotional distance - inexplicably, you suddenly feel completely irreverent to the wellbeing of your lessers. If regular buildings looked like dollhouses before, now they're more like matchbox houses on a miniature landscape. Those tiny moving specs at your feet? You don't even notice them underneath your block-spanning cock.

Some hapless bozo has left all these miniature houses out here in the middle of a public road, to be stomped and crushed by careless passerby. It sure would be a shame if some mischievous soul were to screw with them.

But what fun would be to wreck these tiny houses? Downtown, you spot a cluster of skyscrapers and apartment buildings, which rival yourself in size. They look much more enticing; it's as if they're challenging you with their height. Mocking you.

You stomp your way through the sprawling neighbourhoods, your cock swinging wildly from side to side, whipping streaks of pre-cum across several blocks. Excited, you slam it into the nearest row of flats, only for the entire building to collapse.

Sophie: "Whoops!"

Gotta be more careful if you want to exploit these buildings for their full entertainment value. Thankfully there's a whole bunch of these things next to one another! You kneel on top of the rubble from the previous row of flats and insert your tip into the bottom floor of the next one. Carefully, so as not to disturb the structural integrity, you start rubbing yourself off.

Sophie: "Come on, now... come on!"

While the **** of your ejaculation is diminished after having cummed just moments ago, its volume is not. One by one, you can see cum starting to spew from windows of each floor, top to bottom, until finally the roof of the building is blown off like a party popper full of custard.

Sophie: "Haha, wicked!"

Despite, and probably at least partially due to not having testicles, your cum reserves seem endless. All the better - you can keep fucking for as long as you like! The next building you decide to tackle from the middle floors.

This row of flats behaves entirely differently when cummed inside of. The windows don't break at all like in the previous building - instead, for some unfathomable reason, the walls begin to bulge outwards until the entire building is rotund as a softball. The supposedly concrete building inflates to three times its original size before bursting like a balloon.

Sophie: "What the..."

Surely that's not possible. You consider for a moment. You're not sure if the previous building behaved normally, either. Why would the roof give in first, instead of the walls?

Sophie: "My cum keeps doing the weirdest stuff! What the hell?"

An inquisitive mind that you are, you decide to experiment. You attempt to consciously alter what exactly your ejaculation does. Something so absurd that it couldn't possibly be accidental. You point towards the largest skyscraper in the city, and focus on the idea of... your cum evenly covering the entire surface area of the building, before congealing and hardening into the shape of a dildo.

Sophie: "Alright cum, work your magic!"

Without so much as a single stroke, a huge spurt flies off towards the towering edifice. Accurately mimicking the visual image in your mind, it first splatters harmlessly against the glass walls, quickly spreading across all surfaces, unnaturally enveloping the building like a goo girl's handjob.

Then, exactly as you willed it, the cum reforms the entire building into a rounder, veinier, curved shape. It even assimilates a mall situated at its base into a set of testicles. Never again will you idly quip that skyscrapers look phallic - this one beats them all.

The only problem here is that the damn thing is bigger than yours.

Sophie: "Well that just won't fly!"

With slitted eyes and frowned eyebrows, you again exert your influence on your cum, forcing it inwards even after being solidified, crushing and mangling the remains of the skyscraper down, until it looks just small enough to sit on. And sit on it you do, riding the dildofied structure like a roided-up mechanical bull, splattering your cum over half of the city.

This 'spermancy' could have a lot of potential use.