I changed Q1 to a BC550C and it works ok, the “beta” on my transistor tester was 483 for the BC550C and 212 for the 2N3904. It might have been a little bit louder but it was certainly not striking (the body of the BC550 has to be turned 180 degrees to get the leads right). So, it might make a little difference....
You can try tweaking the little loop some, it can change the reception significantly if it’s really not right.
i could not find a speaker that produced more audio, and would fit, regardless of how many ohms it was rated.
So far I have not found a way to make it a lot louder, I do think the mods make the volume control go quickly from silent to max volume at about half way round with little or no change before or after.
i considered the limited volume as possibly a positive feature for my daughter when I made one with and for my grandson.
i am not bright enough to figure out how to modify or add to the circuit to make it louder than it is, so if you come up with something please do share it on the list. Thanks &