The question might seem odd, but hear me out.
So my question is: should I sell my mini and buy an iPad 4 with 128? I don't like the design and I think it's too heavy, but the retina is screen is gorgeous.
Don't buy a device you won't be happy with. The iPad 4/128GB or iPad 5 could have 1TB of storage, but if you don't like the design or think its too happy, then it doesn't matter how much storage is in the iPad - you won't be happy.