we LOVE that area. Dollywood is a must. And yes, if you go after (I think it is) 4:00 pm... you have 2 hours to do the park, but you get free return admission the next day. We have done this before. You do have to pay to park both times, though.
Find time to at least hike one trail. There is a loop you can drive also, that has a few pull-off spots with old rustic buildings/homes, etc. (I'm not talking about Cades' Cove, although I have heard that is a great place to see also). Stop on the parkway between Gatlingburg and Pigeon Forge at the Ranger station and they can give you a map and show you what trails are suitable (for your ages, physical ability, and weather conditions). There are several go-kart tracks/goofy golf type places... and they are neat, but nothing special you can't do other places. We always have fun, though.
Last summer we took the kids into the WonderWorks (?) place... the building looks upside down from the front... it was really pretty neat. It is loud inside, but the kids had a BLAST and there is neat stuff to learn/do (rock wall climbing, experiencing freezing waters like the Titanic (stick your arm in this thing they have), experiencing hurricane winds, simulated earthquake, learning how pulleys work by hoisting yourself up on different set ups; virtual games; using robotic arms to stack blocks... it had a little something for everyone... even artwork upstairs that will blow your mind (one looks like it moves and you can "see" down different streets as you walk past it)...
We were there for about 2 hours before my husband couldn't take the volume any more, but the kids were still having a blast..
Uber Gatlinburg has some cool "sled/toboggan" things you can do... and you can ice-skate also.
We never go without spending one day doing "nature" activities... take a picnic lunch (Larry's subs, lol) and eat at a park then hike to a waterfall somewhere. There is also horse riding available, if you are into that... I am always disappointed b/c it is not the same as riding your own, but....
Have fun.. and be sure to "walk the strip"... Ogle Dogs have THE BEST corndogs anywhere!!!