I want a 256GB model.
I have a very large music collection, which up to now I've been loading on an aging iPod Classic. I could load it all (barely) on a 128GB model, but it would leave me no room for anything else, or for additions to my collection. I can get by with a new genre "Do Not Sync" and syncing the rest of the collection by genre, but I'm still close to limits at 128GB.
I don't think that Apple will ever sell a 128GB iPod Touch, so the mini seems to be as close to a replacement for my iPod Classic as I'll ever see. And yes, it does function very well as an "iPod Touch Maxi", better than the actual iPod Touch that I keep around for app development and testing.