I gotta say that I absolutely love these releases. Almost all of these have tracks that are either very interesting or essential. I picked 5 up there, but in my mind most of them are worthy of being picked up for die-hards. I will go through all of them and mention the reason they need to be heard (or not).
The Majesty Demos 1985-1986
Very cool to hear the band at the very beginning. I have no problem with production issues, I've heard worse recordings. Worth it to hear the original version of Another Won and A Vision is an early epic that is very good.
When Dream and Day Unite Demos
I love demos, and I love Charlie Dominici's voice. Lots of early instrumentals to dig through here, inluding some that didn't make the album. Worth it to hear Charlie sing A Vision, To Live Forever, and the Beatles Medley at the end of disc 2.
Images and Words Demos
This disc is easily worth the money for the vocalist auditions. An early demo version of A Change of Seasons is the highlight of those, and the ATCO demos, some of James's earliest recordings with the band (amazing)
Awake Demos
Admittedly, Awake is not my favorite album, and the demos here do not offer much in the way of different versions than what made the record. Interesting to hear The Mirror's demo, though, which still has the Lie riff in the middle of it, but was before that was a different song.
Falling Into Infinity Demos
As many have said, this could easily take over the original album. Most songs here had been completely reworked after this, so there's many nuggets in many of the songs that were left out. It has the five B-sides that were on the Cleaning Out the Closet disc, and a 20-minute Metropolis 2 demo. Worth it for those alone, but Lines in the Sand is probably my favorite track here.
Train Of Thought Instrumental Demos
These are fun to listen to, but it's about what you would expect from the title.
The Making of Scenes From A Memory
Very much worth buying. The second disc is the entirety of SFAM with a different mix, and it's very cool to use as an alternate version of the album.
The Making of Falling Into Infinity
Probably only for die-hards. Not much here in the way of "songs" but it's cool to hear the album come together.
Los Angeles, California 5/18/98
As far as live albums go, it's okay. It's a full show from the FII tour, which in my opinion has had way too many releases. This one, the '96 show, OIALT, the Outtakes disc, Five Years... a little too over saturated, while the 6Degrees tour hasn't had much. But it does have some cool performances, including Speak To Me.
Tokyo, Japan 10/28/95
Focuses on the Awake album, but a couple great rare performances, including A Change of Seasons in full with Derek, and Lost Without You.
When Dream And Day Reunite (CD or DVD)
Hands down, the best release. I would get both, just to have the audio, but also the commentary on the DVD. Nothing else to say, it's great.
Old Bridge, New JERSEY - 12/14/96
A Pre-FII show with lots of FII demos making this live album. Most of the songs, including older ones like Metropolis and CIAW, have jams or are different versions. Worth picking up.
New York City 3/4/93
The definitive I&W show. Has all 8 tracks, the original ACOS, a bunch from WDADU, To Live Forever, Eve... A must have.
Bucharest, Romania 7/4/02 (DVD only)
Great show, which bring pretty much every long song they had at the time. Killing Hand, Learning to Live, Scarred, Lines, Home, Glass Prison, Great Debate, Six Degrees. It's only missing Trial of Tears. While the quality could be better, it's still worth it since its the only chance to see the band on this tour.
Santiago, Chile 12/6/05 (DVD only)
Great alternative to Score. No Another Won, though.
Master Of Puppets
Pretty good Metallica cover album.
The Number Of The Beast
Great Iron Maiden cover album.
Dark Side Of The Moon (CD or DVD)
Bonus disc is worth getting.
Made in Japan
Don't like this one, not a DP fan.
Uncovered 2003-2005
Very cool disc. Diary of a Madman FTW.