Even if I have flagged a poster to look at, I will walk away if I show up and can't size it up in a short period of time to see if I want to know more. Good content is irrelevant if it is presented poorly.
I don't know what good content would mean if people cannot understand the poster. That's just crap and you know it.
I do know that having a colorful poster with a lot of graphics is not going to attract people if the title isn't "Really Cool Thing That People Want to Know" or has major name attached if not standing right in front of it.
I agree that the title has to be big enough to see, the graphics have to be legible, and the text has to flow in a logical way, but once those criteria are met, further optimization on presentation often is not warranted.
I guarantee you that people will stay at a poster that is legible and has graphs that can be deciphered even if it's black and white with a bit too much or too little text over a poster that is colorful and has good use of white space without saying anything.
I myself think that the problem of content and the problem of presentation are two very different things with low correlation. I have seen posters with awesome content that were either well-constructed or block letters on butcher paper. I have seen posters with zero content that were constructed the same way, with the same extremes.
In other words, the graph which has "awesomeness of content" on the y axis and "awesomeness of layout" on the x axis is less of a line with a slope of -1 as it is a shotgun blast in my (frankly, not inconsiderable) experience. I have seen where snazz has tried to cover up content, but rare enough that I am not willing to ascribe this to a general rule. I also have seen where a lack of presentation skill has scuttled posters, to the point where the (likely awesome) message has gotten obscured, but this has also been rare. Maybe it's different for different fields, but I can see where playing in the margins is A Bad Idea, no matter what the field.
So long as the "snazz" doesn't get in the way of the content, awesome. Snazz should be what you go for when the content is in. But once it's in, there's no need to denigrate it. It's not as if though facts are being replaced with unicorns.