It's cute. I've been maybe 3-4 times, but not recently. Bought my wedding unity candle in a shop there 15 years ago.
1/2 day to one full day is enough to explore it as I recall. JMHO.
Oh, and I think Ocktoberfest there gets very crowded, so if that's an issue, you might want to avoid that time.
I agree that Anna Ruby Falls is beautiful. And if you enjoy hiking, there's a nice trail between the falls and, I believe, Unicoi (sp?) State Park.