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If you use a dish or other high gain aerial it boosts signal both ways. Also been done with WiFi to 10 km (personally done with a mesh dish only at one end on chimney stack) and RFId tags.
Miscreants and researchers use either truck with canvas side or fibreglass panel.
No boost to power on gadget needed. Indeed illegal power levels on a WiFi airpoint with a regular aerial is pointless as the laptop/tablet/phone power is limited. But a high gain aerial or dish at one end boosts reception. You are 100% correct that purely boosting power at one end of a two way link is pointless, but a higher gain aerial boosts receive signal and improves S/N.
I also have a satellite reception system that uses a 120 cm dish rather than much smaller dishes used in Ireland for Freesat or Sky Ireland. In London they use an even smaller dish for the same Satellite signals. My big dish is so that 5 satellites, including ones beamed at other EU countries, can be simultaneously fed to our satellite distribution system, so that the family in different rooms can watch different satellites at the same time. The 1.2m (120cm) can get signals four times weaker than is possible on a 60cm dish.
Our two way backup internet over terrestrial 10.5 GHz microwave is 13 km path on a system designed for up to 9km, so it uses a 35 cm dish instead of the standard 10 cm x 20 cm printed panel array (actually the standard system uses separate one for TX and RX, but the waveguide at the dish focus has separate 1/4 wave stubs for H and V signals to the TX & RX on the box with panels removed using SMA hardline cables at 10.4 GHz approx). The outdoor box converts to 485 MHz (RX, download) and 40 MHz approx (TX, upload). Then the indoor modem is cunningly a DOCSIS 3.0 Cable modem. It's been running since 2006, though last year they replaced the DOCSIS 2.0 modem. It was our main internet till we got fibre and we still use it for phone calls as well as it being a backup.
Radio Amateurs now bounce 144 MHz digital signals off the moon to each other using as low as 20W with arrays of aerials, though 200 W is normal.
The effectiveness of dish size rises with frequency. Though loss is an inverse square law, the dish gain for a given frequency is proportional to area, thus proportional to square of diameter.
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