I remember wanting the DGP stuff so much at one point. But now, I could not care less if I ever own it. He lost his real window of value in my opinion. :-(
The DGP MT Alien books are better than all other treatments of the subject in Traveller history. One thing I still yearn to have is the unpublished texts of the remaining MT Alien series.
The SSOM is nice, but IMHO, it's a lot of detail you don't really need (and like other such works, it provides definitive answers to nitty-gritty questions of technology that are better left vague.)
The illustrations and fluff text from 101 Vehicles would be a nice asset to have, as would be art and text from the Digest and MTJ.
Grand Survey/Grand Census and the WBH were revolutionary at their time, but now others (First In, MgT WBH) have followed and essentially superseded them.
Flaming Eye is a good adventure campaign, I suppose. But nothing special or groundbreaking.
The DGP MT Alien books are better than all other treatments of the subject in Traveller history. One thing I still yearn to have is the unpublished texts of the remaining MT Alien series.