The problem with such books, especially when developed as a creative blok, is that you get a lot of "why is this race different?" that devolves into either silly, repugnant, or both.
I'd love to see a book, or a return of "Contact!" to S&P, that addresses the existing Minor Races. There are already a shedload of them, and only a couple are obviously "take this other race and tweak one small thing" (the Hlannsai are more Vargr than the Vargr, for example). There are also a few that are bad fits, or incomplete fits, into the Third Imperium setting. The Valkyrie (of GT) and several of the races from T4 come to mind here.
There are a number that are barely beyond a name and place, or which are simply too wierd to use as PCs. The Jgd, J'sia, and those ambulatory plants in Aslan space are in this category. Nice for NPCs, but really, who wants to run a 4-meter-long soft worm?
Then there are the majority with *almost* enough information to run well as PCs or NPCs. Most of the Human Minor Races that are more than a name fit here, as do the Virushi, Ael Yael, Shriekers, and Llellewyloly (in print), to name a few.
Only a very few have had enough written on them, or are coming from easily grokkable fundamentals, to be easily playable. I put the Newts and Ithklur in this category.
Hit up the Chirper link above and dig around in the listed Minor Races. Lots of fun to be had there.