I think in the past Bonnie's had too many people comment "if I'd have known that, I'd have chosen differently" so if you are that type of person, it may be best to wait a bit. I think people confuse a "mystery" with a "sew along". The clues come fast enough a lot of us are way behind by the final reveal, so if someone else waits and then starts sewing, they will still have lots of people to "sew along" with as they complete it.
I'll be honest and say that I don't usually like Bonnie's color choices, but that is a personal thing. However each and every one of her mystery quilts that I've made has found a home with someone that was just amazed at how it wonderful it looked.
I also think that if you are person that does not like "scrappy" then you may want more control of the final results so waiting is good. if you are totally comfortable with the unpredictable of going "scrappy" then you probably will not end up disappointed no matter what, whether you go scrappy or not. I myself love using 6-7 different fabrics, so not really scrappy but not all one either.
It's all about deciding where your comfort zone is - or if you can deal with going completely outside of it for a while.