Dear ramsro,
I respect your opinion. And you're quite right. Sometimes I do prefer blind contest but as long as the Contest Holder has a very good brief. if the contest holder is not specific in the brief, or does not give a lot of feedback, then blind contests can be frustrating. There was one occasion where the briefing was very vague and the CH keep eliminating everyone! Basically, no one had the slightest clue what he was looking for and he wasn't leaving much helpful feedback.
So, Sometimes they're good...Sometimes they're not.
An OPEN contest helps me to see what has already been submitted and what kind of design is rated high enough in a contest And then, I try to come up with something DIFFERENT. But Unfortunately, not everyone is honest and people will rip off others ideas, i know. There are those (people who want to be designers or are just looking to make a quick buck) hit and run kinds, those who like to see other’s designs & steal their ideas. They do minor modifications and submit designs to the contests claiming they are theirs. In that case we report them in the designers court.
A blind contest for me is like It's like playing basketball sans the scoreboard and the referee won't tell you the score until after the ending. 
So, its good and its bad.
Warmly,
akhtanbed
(Please pardon my English, I know its bad. Its not my first language
)