I don't know how accurate those stories are though. I would not call them impossible, but a plane must be really extremely low (about 10 meters) to hit trees and telephone wires. At such low altitudes they would have to drop bombs with small parachutes (lest they be damaged by the explosion of the own bombs), which I know had been done by the US airforce in the Pacific theater while I never heard about this practice being used in Europe (just because I never heard about it doesn't mean it didn't happen of course). However I consider it very unlikely that a plane (a wooden plane even) would hit telephone wires or trees so directly as to bring parts of it back. Not only would those parts have to be really sticky, but it is also extremely unlikely that a plane would make such forceful contact with a solid object at a speed of several 100 kilometers per hour, at an altitude of little more than 10 meters at most, and not suffer such extreme damage or unbalancing as to return home. Just think of the immense force of even smaller objects hitting cars at a much slower speed. The planes would not have hit any telephone wires for sure because in Germany they were under ground back then, same as today. There are some above surface electricity wires in very sparcly settled regions. I guess it might be possible, but something extremely exceptional. Where did you read about it?
In any case flying at low altitude was not the reason why the Mosquito wasn't easily detected by the radar.