I have last year's pink poly cover for the Mini.
Yes, it gets dirty easy. The light colored inner microfiber picks up stains when I prop the Mini on things with the cover folded flat against the back, including dye from my jeans because I prop it on my legs quite a bit. The front picks up stains from all sorts of things regularly.
But--
The front is EXTREMELY easy to clean with a damp cloth, or a bit of window cleaner if it's really a tough stain, and after a bath, it looks the way it did when I got it. The inside I've washed with soap and water; it isn't perfectly back to the original color but it's presentable. I don't notice any significant change in feel to the front or back of the cover.
I'd buy it again. It's useful, and it still looks pretty good for a 15 month old cover that's seen heavy use!