We spend a week in the fall and the spring in Fredericksburg. We've done the Willow Loop and while there were quite a few wildflowers, the loop takes forever to get around and we've seen better. Plus the road is very narrow and your are encouraged not to stop as it blocks traffic.
In Fredericksburg, we normally stay at Lady Bird Johnson Municipal Park run by the City of Fredericksburg. Full hook ups run $30 a day or $175 a week. I've also heard good things about the KOA. There are also several Texas State Parks in the area that are nice, including Blanco and Pedernales.
Between Llano and Brady there are tons along with a couple of bald eagle roosts and there are safe pull outs where you can stop and take photos. According to Texas Country Reporter, the Lady Bird Johnson Wildflower Center in Austin was voted the best in the state.