"Trouble is, even if it made sense economically, which is dubious, it requires a huge rectenna for efficient power transmission."

This *may* be true.
But there are a lot ways to do something.
And I'm not going to attempt to engineer it, but large doesn't necessarily mean massive. And/or perhaps lasers and higher frequencies could be used to transmit from GEO via LEO and/or stratospheric platforms thereby requiring smaller antennas GEO. Or perhaps, we don't get power from Space [at least in the beginning] but instead use power generated on Earth which is transmitted via the space environment. Or perhaps the large ground rectenna typically part of these ideas, is made even larger.
And there are undoubtedly other ways which can be discovered that would make it more profitable.

It should be kept in mind that my heart isn't really into devising ways to beam power from space to Earth in near term. Rather I see it as something very doable in longer term [maybe a bare necessity/absolute requirement in 100 years, almost inconceivable if not in 500 years]. What I think is doable in short term is establishing a market for electrical power in the Space environment for use in the space environment [beaming not necessarily required]. So, I would suggest using electrical energy in space to make rocket fuel from water mined in Space, and rocket fuel is used in space. This of course would "evolve" to power being beam to earth surface- if power in space was cheap enough to allow exploitation of the earth market.

And if you must import stuff from Space, I have few ideas, one I favor is importing Moon dirt- something at the moment that is more valued than gold or even the finest diamonds and if the total quantity of Moon dirt imported is less than 100 tons per year, then it should remain around the price of gold lb for lb [anything which only has 100 tons available per year globally is pretty rare stuff { gold adds in order of thousands tons and diamonds are around 100 tons yearly}] and of course there is some scientific interest in the stuff.