I think it was worth it. The first time I drove the entirety of 64/40 I kept saying out loud (and to myself) "Woooowwww!!!"
Which part of Clayton are you talking about? I used it along with Forest Park Pkwy during the renovation (and took 44 as much as I could, too) and found the increased traffic annoying but tolerable.
See, lately the riverfront has been worked on: MLK bridge one weekend, 70 off Poplar Street bridge another weekend, and those have been the latest headaches. But so far 64/40 is super duper...especially when you get near Brentwood and 170. That whole exchange is soooooo much better than the mess it was before.
Oh, and the Kingshighway exit is much much better too.