OP- Congratulations on your upcoming wedding!
Here are some photos of the premium campsites at Fort Wilderness:
Here are a couple shots of empty premium sites on the 400 loop:
Here is a premium site on the 500 loop:
You mentioned that in looking through photos, you couldn't distinguish between the various levels of sites. That is because there are only three things that make a premium site premium:
1. The sand pad that you see on the full hook-up and preferred sites is paved with concrete;
2. The grills have a lid and a shelf (except for some reason the grills in the 500 loop are missing the shelf); and
3. The premium sites have the square picnic tables that you see in these photos, instead of the traditional rectangular picnic tables that all the other sites (and the cabins) have.
That's it.
As all who have posted have already said, the main reason why some folks prefer premium sites is the extra pavement. If your dad has a big trailer, he might appreciate it.
But, for tent campers and those with smaller trailers (like me), I absolutely do not think the premium sites are "worth it." Typically, the price difference between a partial hook-up site and a premium site is over $35 a night. It is not worth it to me. Think of all that you could do at WDW with that $35. And that is for one night. If you are staying a week, you are talking about a significant amount of money. But, the price difference between a preferred site and a premium site is typically about $11.00 a night. That probably would be worth it if there is a need for extra space.
The last thing I will add is that it might be cheaper to get your Dad a room at the All Star Resort than to pay for a premium campsite. The Fort ain't cheap. You might want to check on that.
Have fun whatever you decide to do.
TCD