I would get another Mini. I like that I can have it in a cover, my stylus, and a keyboard all in my coat pocket. So portable!
There are different chips in each, but honestly, I'm running a DAW called Cubasis, and I have no problem with it and it's one of those apps that would really benefit from the extra power.
Some apps will give you extra stuff to use with the bigger iPads, like more layers, bigger image sizes (but you can't complain when it's like, the Mini can export a 50x50 inch image, and the iPad 5 could do a 80x80 inch image for example), but it's really like exotic benefits that you probably won't even need, hahaha.