Let's say, for a moment, that I have a moderate pile of metal I want to sell. I don't care about selling it to the very highest price bidder - getting 23 credits per ton instead of 21 credits per ton just doesn't register as important, especially if that would require significant travel through hyperspace. What I do care about is selling it to somewhere that actually has a demand (so I get 21 credits rather than maybe 6), and I can't find any way to figure this out short of already knowing which planets have which industries. We've got a planet info page in the intel screen, but all it shows is conditions, not industries (or demand/supply information).
Alternatively, a useful feature would be to have not just 'five highest prices' displayed, but also 'prices at all planets that are in-system'.