If the extras are better than the film, I wouldn't buy it (or would sell it on Ebay asap)! Not talking about you, but I do think some extras attract "collectors" of stuff rather than just fans of the film itself.
I sure wouldn't have bought the BD if I had known! But I buy a lot of BDs just because somebody (reviewer, the public [gasp!], friend, etc.) says the film is good. When I don't have an opinion of my own, I usually wait until it's very cheap. Yes, there's the odd bit of disappointment, especially when a title has been built up until it's great in my mind...then it isn't. Then sometimes I go behind the scenes to see what I'm missing, when I get a glimmer of what might be there to capture me. After that, sometimes the next time I like the film a lot better, often not.
If I don't get a sense that there's anything at all to the film that's going to make me like it, it's just not for me, then I don't even bother with any of the extras.
I almost never listen to the commentaries. Except sometimes I do for TV comedy series, mainly because they're short and usually entertaining, not because I expect to learn anything...