At the moment I'm just doing the worlds I need to fill the holes in the published adventures as I run them. The ones on my "needed but not started" list are...
EA 01 (finished)
Galik 1306 C437678-8 Ni 932 X G2 V
Khirliish 1308 C110400-D 940 X K4 V M5 V
Broad-C 1407 B76A636-B Ni Wa 220 X G5 IV
Berdane 1509 A551378-9 Po 531 X M2 V
EA 02 (anyone who does these by Thursday is my hero)
Siigi 1714 E594646-3Ag Ni 612 X M9 III
Miller’s Reach 2218 D344348-6 821 X G7 V
Am 2319 C110513-7 223 X M9 V K1 D
Aapizishga 1913 B262653-A Ni Ri 403 Cs M3 V
EA 03
Se 1903 B210351-A 304 Xx F1 III M7 D M7 D
LUNBER 2003 C265ACH-9 704 Xx K0 V F6 D
DREESEN 1906 D343985-6 In 703 Xx M1 V M3 V M8 D
In the medium term, I'm thinking I will concentrate my game on the area between the Stoner cluster (book due), and the Starfall cluster (book also due), which EA1-3 also touches. Say everything within 10 parsecs of Bubi (1810). I'll probably fill that area out gradually, most likely working from the spinward/rimward side. So if you want to avoid duplication...
That's assuming I don't kill the PC again, of course.
What I go for when I "do" a UWP is the current state of the world -- people (including me) tend to write a huge history to explain the weird UWP then collapse exhausted; they forget that adventures happen in the present, and that setting history is of interest to collectors and authors rather than gamers.
Info on politics, starport, any unusual law/prohibitions, and unusual trade opportunities are all good. I also like to set it in context with its neighbours. Astrophysics or ecological stuff are nice to have, but they're generally fluff (i.e. they don't normally affect play) and I just don't have the time for fluff what with running a game. And I'm particularly looking for any tensions in the setting, i.e. reasons for a patron to need adventurers. If I'm going to post a world, rather than use it and discard it, I like it to have at least one "hook" -- something a GM will read and think "I could get an adventure out of that".