To be fair, while a drop in ratings could indicate a loss of quality, it just as easily could indicate something else. BSG, especially the new one, fits a very specific taste that not everyone will be into. It literally depicts a world where life's a bitch and then you die. The show may not fit a lot of tastes, but that won't make it bad either.
Though, I doubt the hiatus helped either, as you will not that the very first major drop came after the first hiatus. The lack of change after the second big hiatus shouldn't be looked at too closely mainly because the ratings were already scraping the bottom of the barrel. The hiatus may have knocked the ratings down here, just like I'm pretty sure it did to Jericho
. There are very serialized shows, and they don't work well with monster-gaps in them.