why is this going to broadway?
Paul Blake, producer and book writer, loves Cole Porter, and has loved Cole Porter most of his life (he mentions listening to cole records in the 1970s), and wants to put a Cole Porter Musical on Broadway and fulfill a 20 year plus dream (i assume the dream vision pre-dates the muny production in 2001. If Beautiful had NOT been a huge success, I doubt there would have ever been another presentation of this show.
Beautiful has grossed around $200 million in ticket sales alone, and continues pumping $800K a week, so Blake is playing with house money and then some at this point. Other co-producers are likely hoping Blake and director Bruni will re-create some of the financial success of Beautiful, which pretty much everyone on this thread agrees won't happen.
Why a preview if no big changes?
The show was updated and changed significantly from 2012, including a completely different cast, director, script re-write and some new songs, so it would make sense to have an out of town tryout and shakedown of the new team, sets and material.
They are surveying every ticket buyer who buys online, so maybe they are seeing something in the consumer feedback that has made them comfortable in the material as presented, or they know they are opening in early fall vs late and are focusing on minor tweaks and changes.
I wouldn't invest money in this production, but I'm glad its being done with the caveat that I agree with many it would have been really interesting to see what a few great songwriters could have done with an original score..