Hi David,
Generally it is understood that the quality of the radio determines how "powerfull" the receiver is. Just to straighten out a few misconceptions: The "power term" should be replaced by "sensitivity"
The better the sensitivity, the longer the range of reception. Given all else to be equal.
Transmission power is important as well. However both are subject to an overall important item. The Antenna. A mobile unit is confined to a small aerial and therefore range is limited. A base station can have a large antenna, that improves the range and number of stations received.
Imagine an antenna to be like a funnel gathering raindrops. the larger it is the more water can be collected.
Years ago in the Army, a unit attempted communications (coms) with a 400watt radio. over 200klms. very limited success. I had decent antennas setup at both ends. Reliable coms was established. I further tested and reduced transmission power from 400 watts to a quarter of a watt. Comms was still maintained. Showing the importance of large antennas.
There are further stories where this happened. Australian Army up near Townsville. The officer wanted good coms. on an overnight camp. We were in APC's (Armoured Personell Carriers) I rigged up a temporary antenna to a large gum tree. This established good coms with outsiders. USA military police in Korea. We simply changed channels to avoid confusion between the two armies. My boss was duly impressed, but that was just a small part of my job at the time.
So David, get the biggest antenna that you can and you can listen to the low power stations around the world.
Cheers