I have found the quality of the Disney parks dress to sometimes be better quality than Disney store, but often (IMO) close to the deluxe dresses. However, I have found that i often prefer the look of the deluxe dresses to the parks styles - it's definitely worth a trip to google to see how they look. I was not blown away with some of the park's versions of Rapunzel and Ariel, TBH.
Truth, however, is I have never found the quality to be THAT much better than the nicer Disney Store ones. DD7 has a Rapunzel wedding dress from a trip we took almost 3 years ago and it's held up better than a parks dress a grandparent bought her. Also, I bought her the standard store Elsa dress with a coupon for $40 and just can't see it being worth double the price for the deluxe or more for parks. I think it all comes down to what you see is being worth the value. Personally, I cringe at paying the $50+ for my daughter's dance costume and can't bring myself to pay upwards of $100 for a Disney dress that she's going to be trouncing around the park in! But, my daughter is also a tomboy in a tiara so she is a lot rougher on dresses than some...