i think they are simply two devices for TWO DIFFERENT purposes. A touch to me is largely a portable music player. 100% of it's point is a to be portable, fit in my pocket, so i can listen to music while i'm walking around target not buying stuff, sitting on a train, etc. I'm not a big game player so that's not really a big deal. I use my portable music players instead of a cd changer in my car for years. An ipad mini is simply too huge for that. it cover my vents, my dash controls, my ac controls, it's dangerous as it would be in line with my gear shifter. Not saying it's not doable. I know people do that. It's not for me. I got a nice cradle for a smaller player like a touch. I use my iphone, (same size as touch) for gps. I's smaller and less gawdy in a car then a mini would be.
By contrast the selling point of a mini and a ipad are that they are larger form factor tablets. I'd do tablet stuff with them. and specifically things where the larger size matters. Like watch movies on a plane flight. i've done that on my phone but only cause my laptop broke and i didn't like it. i don't watch video on my phone. I say phone cause it's the same size as a touch and i don't actually own a touch. Reading books, i have ebooks but i never read them on my iphone size because the screen is too small. I'd probably do the same with a touch. By contrast i'd use a mini to read books, magazines, etc where the larger size screen is much more conducive to reading.
that's just me. But for me a touch is and ipod. Its portable music for my pocket. an ipad mini doesn't fill that role.