The Premium kits are old Dragon kits, reworked to varying degrees, and with extra parts added. For example, their old, original Panther Ausf. D was pretty much "all plastic". You got their old style tracks molded on the sprues, and while the kit had seperate periscopes for the turret and hull, they were molded in grey plastic along with the rest of the kit. The gun barrel was plastic, and the tank's torsion bar suspension was molded to the lower chassis.
For the "Premium" reissue, Dragon gave you a new, larger decal sheet, a metal barrel, some basic photo etch for the engine deck screens, a clear parts sprue with the vision devices from the old kit now in clear, new pre-cut Magic Tracks, and a new chassis with individual suspension arms. The kit is 80% the old kit, with some improved parts added and then the metal, etch, etc.
The "Smart Kits" are generally new tool kits from the ground up without much extra outside of the plastic parts. Newer smart kits have more photo etch, but the idea is to have basically a highly detailed but essentially all plastic kit that is quicker/easier to build. One of their first Smart kits (the Aufklarungspanzer 140/1 came with some pre bent photo-etch grenade screens for the turret and that was about it. I dont think the Smart Panzer I had any photo etch at all or just the muffler screens.