Up1ter does great work, and you've done a great job with this accompaniment. Choosing a vector art for a minimalist style compilation is probably the best you could have done here. Anything solid would probably overshadowed the backdrop and looked far out of place.
I'm a big fan of the font choice, too. Though, I would have left the "f" lowercase. Without a period, a capital "F" just creates a sense of lacking when you're looking for that period.
There's one of those sparkly things behind RD's ear that I can't tell whether I like it there or don't like it. It lines up with the purple in her hair and gives that portion of the image a cut-out or almost mosaic look. It's both disturbing, but drawing.
Providing a center orientation for Rainbow Dash, the lettering, and the color/lighting intensity was a good idea. It displays a sense of command, forwardness, and a demand upon your attention.
I'd love to see high-res versions of this for desktop backgrounds... 1280x720, 1280x800, 1680x1050, 1920x1080.
I'd also like to see a line of these for every pony, with a motivational for each of them.