Hi again!
I don't know why you "get the feeling these little greetings of yours are less than genuine?". You are free to believe what you will. On topic, I see your point, as things are relative, but relative to what? To me, the most important reference here is Skyrim's orginal price tag. If Beth managed to sell 300 hours worth of content for 60 bucks, I think it's reasonable to expect 20 hours for less than 20 bucks. For Skyrim, Beth had to develop the Creation Engine, Radiant Story and all the tech. As far as I know, not so with Dawnguard. The same applies to landmass. Do you see what I'm getting at?
Relative to entertainment in general. You are looking at the wrong way, by trying to make a deductive comparison to the 300 for 60 thing.
I see the 300 / 60 deal as just that. One Hell of a deal. I will gladly pay 20 for the extra 20 hrs. I will promise you I will get more than my monies worth.
In closing...will you buy it? I think that answer is probably, yes. I may be wrong...