If U2 were to release a 4 disc box set, do you ask the proprieter to cut it up and just give you the last disc? The one with the rarities on it? Just because you already own the contents of the other 3 discs?
For that matter, did you buy the Best Of Disc 1980 - 1990, even though you had most of that stuff on CD already? I did, because I wanted the B-Sides on CD instead of relying on a copy from my record player.
The digital boxset is expensive, but it is a good value. 37.5 cents a song (if you do the math for 400 songs, not the 446 that you download)
A 12 track CD in the mall can you run you $18 so that's about $1.50 per song. So, in this scenario, you're getting 4 songs for the price of one and you're getting it in the best way. And don't forget that in additon to the Rarities disc, you also got 2 concerts that had never been released commercially and the new album.
Let's price the two concerts at $20 a piece and the new album at $15. That's $55 right there. The rarities and early demos would add another $20. That brings us to $75, or half the price of the box set. And that still doesn't include the b-sides and singles that have never been available in digital format before.
I would defend the pricing because compared to a lot of other bands this is a really cool offering.