It would certainly be wrong to make it TNG Happy, but, I wouldn't want it to be NuBSG depressing. It could certainly have the dark moments of NuBSG, but, you've keep the Avon wisecracks humor in it, to keep it from getting too depressing. I think the darkness of DS9 or B5 would be fine, just make sure that no matter how hopeless things get, that you keep little bits of humor
Blake's 7 was a very dark show to begin with. Take Killer
for example. The entire planet's population is wiped out by a plague, but Avon is only concerned with the theft of the crystal.
Or at the beginning of Star One
, when the Nova Queen collides with the freighter, killing 4000 innocent people and the resulting crash destroys half a city on the planet below.
This ignores all the incidents of Federation atrocities (like the massacre at the very start of the series, or the pacification drugs used on civilian populations throughout the show).
Humour can and will be used, especially if Vila stays as he is.
My only concern is how they handle the Liberator. She's an iconic vessel, and Zen's reference panel - despite looking like a dance floor - is still cool.
I absolutely hated what they did to KITT in the new Knight Rider series.