Star Trek might go DS9 dark but not BSG dark. Don't blame Trekkies for this - it's brand management and it's how corporations keep popular products viable for decades and even centuries.
I'm not sure if that analogy works for TV shows though - seems to me that the more they stick to the formula, the more likely that it will become irrelevant and.....well.....formulaic and the quality drops
Isn't that essentially why the show went downhill and needed to be rebooted for the film - because outside of the fan base, people had got tired of the same repetative storylines and characters
If a new show comes along, you, me and every other trek fan may think it's great but if it doesn't stand out as new and unique then those who are not already fans will have no incentive for watching and this is my worry - if trek fans are the only people interested then ultimately the same thing will keep happening - it will get cancelled over and over and gain a reputation for being a show "just for trekkers" and the makers just won't see the benefit of making a show for a small group of avid followers
as far as i'm concerned, the next star trek show has to become a show that people talk about (like sex & the city, the wire, the Sopranos, mad men etc) and the only way to do this is to have staggeringly brilliant writing and inovative ideas and originality - something i have not seen in any star trek show since the original to be honest (it didn't matter before i think if star trek is to survive, it needs to matter now)