Never had a Premium Cabana, but have used a Standard Cabana a few times before and found it well worth the price - the ones we used were located near Cutback Cove, but I don't think they are there any more; from the sounds of it these ones might have been moved to Walkabout Waters instead. As far as I can see from the Aquatica website, the only advantage of the Premium is a more central location, slightly better quality furniture and the option of food delivery (but you still have to pay extra for that).
Just to have your own space reserved for you in the park is a massive benefit and add to that the free towels, locker, ceiling fan and bottled water and I think they are great value. The first time we rented one, the park was half empty and they were selling them off cheap at the gate, so we thought "why not?" and our experience was that good that we've booked one every time since - at full price of course!