I'm in the US but my house is still ~200 years old. I've had a couple of major renovations done and have had networking cables pulled when walls were opened up anyway for electrical and other reasons. (WiFi was less widespread and mature at the time.) I added speaker cables as well. But barring real issues with using wireless in conjunction with Powerline or whatever, I'd never want to open up walls just for the purpose of adding Ethernet cables.

Personally I've run CAT5 when I've added sockets or rewired after moving in. I've yet to own a house, esecially older, that's not been greatly lacking enough sockets and I don't want everything hanging off an 8 way adaptor.

With wood floors you can usually avoid much impact and just run cables under the floorboards.

You could do a wireless point to point bridge in most places where running a cable is difficult. It is much more reliable than relying on an omnidirectional wireless access point over that distance.

Do you have data to back up this claim? In my experience, the reliability of the hardware has nothing to do with the antenna and everything to do with the software running on it.

Collisions between a directional link at short distance and other things using the spectrum are minisicule. It is like using megaphones to hold a conversation at a distance of say 10ft. It does not matter whether you are in a crowded area with everyone talking. The megaphones will drown out everything else. Using omnidirectional antennas is trying to talk without with out the megaphones. The difference in signal strength is what makes the wireless link with directional antennas more reliable than the one with omnidirectional antennas.

I don't understand how Americans complain about non-hidden cables, but live with crap like exposed conduits in the hallways, exposed circuit breakers in rooms, and ten layers of ugly paint over everything.

I think you answered your own question! I'm already at a breaking point of "mess" just by virtue of living in this (relatively speaking, pretty decent) apartment. The less mess I'm adding to it, the better.