I disagree about Smart/Exum. Exum has a TON of benefits over Smart. Athletiism, height, court vision, Passing, ball handling, ability to finish over length, post up game, age.
I think both are great players and both have the potential to become All-Stars, but Exum's ceiling is far, far higher. Whether he'll ever achieve it is another question.
As for the original question, hell yes. I would trade 6+17 for #4 in a heartbeat. Embiid, Wiggins and Exum are all to-way players and physical freaks with sky-high potential. Even if those guys don't develop superstar offensive potential, they are almost certain to become elite defenders. There's minimal risk here, except for Embiid (with the injury concerns).
Parker has less potential, but he's the most NBA ready of the lot right now and could potentially be Boston's #1 scorer from day one, allowing Jeff Green and AB to slip back to their more natural complimentary scoring roles.
Either way it's hard to go wrong with any one of those guys.
If we couldn't make he trade then I'd still be pretty happy with Smart or Vonleh as a consolation prize (which is why I'm pretty happy with #6) but no question that I'd be incredibly cheerful if we did manage to move up to one of those guys.
Utah are in a great position a #5 because there is a pretty decent chance that one of those top 4 guys drops down a spot (Parker over defense/conditioning concerns, Embiid over injury concerns, Exum because people haven't seen much of him) but I think if one of those guys does drop, Utah will snap them up. I really doubt any of those 4 will drop to Boston at #6.