You say "half of the album" but this is the album. All that other stuff was left off for a reason.
That's the fucking problem with CDs. Everybody decided that since they could hold 80ish minutes, then they should. I may be a purist here, but I hate when reissues have all kinds of bonus tracks stuck right after the album ends. They could at least have 30 seconds or so of silence to help you cleanse your palette, y'know??
I guess I place a lot of trust in the band/artist, and that they wanted the album to contain that many songs as a singular piece of art. I think it's why Beck's The Information bothers me, because he's essentially saying "here, you take all these songs and stickers and you decide what the album should be." That's a fun experiment and all, but it ends up making the individual songs better at the expense of watering down the album as a whole.
I guess what I'm trying to say is, if your album is longer than 50 minutes, you better have a damn good reason to be that long. Otherwise, split it into two albums.
Which brings us back to Radiohead. I'm almost positive that somewhere they said Kid A and Amnesiac were originally going to be a double album, but decided to split them into two releases after some debate. I agree wholeheartedly with this decision, and it's why I like the idea of them releasing In Rainbows in a lean, pure form and then giving us the option to go whole hog with a disc box. Personally I think it's harder to make a great album that's short than a mediocre album that's long.