To me, "Dream ON" is like "Bold & Delicious" in that I'm glad she doesn't have a lot of songs like it, but... she's Ayumi Effing Hamasaki. She can afford to do whatever she wants, and it's fun watching her have fun while not giving a crap about maintaining the status quo--if only for one single.
I wouldn't mind a self-indulgent mini-album. I'll start to worry if her next full-length album full of "Dream ON"-esque collaborations.
That said, I think "Dream ON" is an ok song (not nearly as good as "B&D"
); the only part of "Dream ON" I really don't like is the ad-libbing (?) in the middle. There's a part where it sounds like her voice cracks, and I can't imagine why she would leave that in the final version. It bugs me every time I hear it.