Yep, I've used that as well, but, as you say, it's just very bad for impact resistance. I think the sweet spot between weight and durability might be ABS or something like ASA.
Yes and there is foaming ASA as well which is almost as light as foaming PLA. But I can't print ASA well on my A1 and the weight penalty was still enough that I didn't try, given the mission profile of flight time.
Did I dream or is there even foaming TPU? TPU in general seems almost indestructible to me so should be good :)