Hm, premium in what sense? I know that the SP's retail for more than the other Free Chukkas to date. They also got Nike's White Label box treatment. Apart from that and the difference in colors, what factor in your opinion causes the SPs to merit being called "premium"? Correct me if I'm wrong, but as far as I can tell based on images and technical specifications, the SP Uni Golds are essentially made using the same rubber compounds as its brethren. Perhaps it could be that the inferior pair you have is a bit flawed?
In my opinion, I'd actually be more biased to call the SP Gold's more premium just by colorway alone and the better packaging, but I'm a bit skeptical that they'd be made with better materials. Better craftsmanship perhaps, but not sure how much more premium Flyknit and the Free outsole can get.