Space Opera is easy to define. Any drama set in space or on a world requiring space travel to get to can be considered a space opera. The key word here is "drama." The shows that really don't fit are the comedies, because, y'know, they're comedies.
That's hardly the agreed-upon definition of space opera. What's lacking there is the nature of the drama. The term "space opera" is believed to be patterned after "soap opera," one of whose essential defining characteristics is cliched melodrama and which as a term dates from radio days, and after "horse opera," a somewhat broader and nuanced concept which at least encompasses western adventures that are formulaic in nature.
By extension, "space opera" consists of adventurous exploits with heavy doses of formula, but in spaaace. I believe that most would agree that
Flash Gordon and
Star Wars are examples of space opera and that
2001: A Space Odyssey is not.
Practically all sci-fi TV shows set in space seem to be space opera, perhaps because that sells better than other subgenres.
Star Trek, Battlestar Galactica, Babylon 5, and
Quark (there's a comedy) are all space opera, most would agree, I believe.
It might be worth discussing whether
Futurama qualifies. I think it does, but I'm not sure how much of a consensus there would be.
Humanoid Cylons were a cost-cutting measure.
Perhaps they might have been that in the manner by which they were originally conceived, but the premise that that's all or even just primarily what the nuCylons were to nuBSG ignores the facts that their humanoid form was integral to a great many episodes and really essential to the series as a whole. You had stories that were groundbreaking for the genre that would have been impossible to tell otherwise, such as those involving the torture of Cylon prisoners, which without humanoid Cylons would have lacked allegorical significance with respect to the real world torture of prisoners. And you also had elements that were essential to the overall series such as the Final Five and other Cylon infiltrators among the humans, which again would have been impossible without humanoid Cylons. Whatever the motivation for creating the concept might or might not have been, the concept was essential to the series. These are all matters of fact.
Whether you liked the concept, whether you thought the stories that were told using the premise of humanoid Cylons were good or interesting enough to justify adopting the premise, these are the matters of opinion, in which no one can claim authority.
Again, you don't have to like them, but the idea that a cost-cutting measure was what the humanoid Cylons were, as if that's even just what they primarily were, that's just factually incorrect.