In general, I prefer the designer item to the "inspired" versions or the, er, knock-offs. In most cases, the designer items have better craftsmanship, more detail, and fit better -- so I don't mind spending the extra money if I know it's a piece that can make a statement, the quality is high, it fits well, and I can't find a version I like more. And if I can come up with enough practical reasons for owning the piece (as much as I would have loved to wear the $8,000 Marchesa gown to prom, I could never justify it to myself or my parents).
So, while I was in China -- I found a pair of similar sandals for the Chinese equivalent of $100. They were made of real metallic green leather and I preferred the brass bows on this pair to the leather bows on the original Marc Jacobs version! The craftsmanship on these sandals is excellent -- they're extremely comfortable and high-quality.
This is one of the few instances where I prefer the "inspired" version to the designer original -- even if both pieces happened to be the same price, I'd still choose my metallic green versions from China. However, I am still fatally in love with Marc Jacobs in every possible way.