I scan every system thoroughly, detailed surface scans, etc. Many of the landable planets I will go down and drive around a while, if only to get some nice screenshots.
I realize the point isn't the cash, but I've heard tell of people making multiple millions in one trip. So, having spent a significant amount of time exploring, I'd anticipated a sizable return on my efforts. I'm not sure how many systems there are per page. Page 10 had only 1 system on it, and there were around 5 systems among the 10 pages that didn't sell because they were too close to the "home" system where I sold the data. However you slice it, that's a lot of data.
Now, I didn't come across anything really interesting on this trip. No earth-type planets, almost all ice moons, everywhere I went. I did visit the planet with the Ancient Ruins (I don't recall the name), where I picked up a few artifacts and whatnot, but even that stuff was unimpressively valued when I sold it on the market.
All in all, a disappointing return, but I did get some very nice screenshots (see the epic screenshots thread for some of them!).