[Arran]

I have not found loop antennas to perform any better in terms of gain or noise then a long-wire and a proper antenna coil around here, most of the interference is power line noise and hash that only a power line filter could fix. Whenever I see something like a random loop antenna tacked onto the back of a pre war radio I put that in the same category as most of the aftermarket phono jacks I see, they were usually added by some weekend warrior who assumed that they were making some improvement but didn't really accomplish anything useful.
I'm not arrogant enough to second guess the factory engineers, at least of the larger manufacturers like RCA and Philco, they had all the specs and resources at their disposal to design the tuned circuits in their front ends and knew what to match with what. I know that many like to thing that interference and hash is a new thing but if anything they had more of it 70+ years ago, brush motors, automobile ignitions, diathermy machines, street cars, and to make matters worse most house wiring did not have a ground once you got past the fuse box. To some extent the engineers did take this into account, of course they could not have taken more recent trash like cheap switch mode supplies into account.
Sometimes, then as now, the interference can be caused by defective street lights and pole transformers, such things can be tracked down and reported to the local power company's service department. Usually when a pole transformer starts to cause interference, or produces whacky voltages, it's a sign that something is about to go.
Regards
Arran