I make it up that way from time to time to get in some training rides. One thing I've been doing lately is parking at the School beside the park in Valle Crucis. You can do 3 nice loops from there and each one is around 25 miles or so. It let's you use your car as a Sag stop.
The 3 loops I do are George's Gap-head over to Sugar Grove from Valle Crucis and do the last 20 miles of BS&G. The next Loop is up Hwy 194 to Banner Elk and back-you can ride on over and do Beech but I'd really avoid it this time of the year. If you don't get bummed going up you'll not enjoy coming back down with the ski traffic. The third loop I do is to ride from Valle Crucis and do Shull's Mill Road to Hwy 221 to the Parkway and then back to Valle Crucis via Shulls Mill.
Another option is to look on Gaston County Cyclists website for the Blowin Beech cue sheet. It starts in Blowing Rock and uses a lot of the same roads I mentioned above. It's only about 50-55 miles but you feel like you've done quite a bit of climbing over those miles.