I think what's a real shame about the Ferengi episodes is that, at some point they just went totally overboard with the goofy, "funny" side of them instead of building on some of the more (IMHO) interesting aspects concerning their culture and society.
They actually started out pretty well, I think, when the Nagus was first introduced. And they did have some really good material such as "Business as Usual" later on but far too little IMHO.
I think the Ferengi worked best when they managed to balance the drama with the comedy. "Business as Usual" is a prime example, really, because the subject matter is actually pretty tough and well dealt with throughout the episode. At the same time, the way Quark handles and resolves the issue is hilariously funny (in a slightly sinister way) and could only be done by a Ferengi.
It's when the drama gets discarded ("Ferengi Love Songs", "The Emperor's New Cloak", anyone?) that the Ferengi episodes just become totally annoying and a waste of screen time in my opinion.
Having said that, there's also the odd episode such as "Little Green Men" that manages to simply be fun - though some of the comments on our time and culture shouldn't be forgotten.
Finally, I have to comment on "The Magnificent Ferengi". Yes, I've seen it, and more than once, mind you. And, frankly, I don't like it. There's some funny moments, I think, but overall it's a waste of two perfectly good (if not excellent) Vorta characters for the sake of pretty mindless comedy. Don't get me wrong: Mindless comedy can be terrific. It just shouldn't result in a price to pay that IMHO is too high.