For me, Endless Sci-Fi Roguelike concept is already "interesting" in itself. No need for USPs or such. I love a SF setting and majority of RLs/RPGs seem to be stuck in the fantasy territory. As for the "endless" thingy getting boring, not a problem for me - if the game can keep me entertained for a long time it`s a mission accomplished anyway. And if this is a roguelike I`ll probably die a lot and so on...so no worries there. Plus, you can always put in some major "winnable" quest in - and keep the universe going on endlessly even after completion. And/or have a scoreboard...and a retirement option - I`m thinking Pirates! now - where you get not only a high score, but also some status description for your trouble.
Starflight is one of my favourite games of all time, and what you describe here seems to have lots of similar aspects. In fact, it seems too good to be true almost, what with the massive scope - random missions, endless weapon upgrades, planetary exploration, asteroid mining, ship boarding...Lawd! Plus, it`s an RL. If you pull it off, it could be a major hit.
One area that needs special care in this genre is space combat itself. For some reason most of the old classics, while totally awesome in other aspects, choose to go down the arcadey, real-time route for battles. So I hope yours is turn based...
Some other titles to land on & mine for ideas: ASCII Sector, Strange Adventures in Infinite Space (that one`s actually free now, wow). Space Rangers 2 is very original , though not an RL.
Finally, where can I find KlingonRL? The database`s down...