Claris vs Sora shifters
The Sora groupset does indeed sit above Claris in the Shimano pantheon. Shimano carefully engineers each level to be incrementally better than the one below it, in terms of features, weight and quality of materials. 

You should be able to feel a difference between the two groupsets in terms of shifting. An extra sprocket in the rear is nice to have as you will be more often able to select an optimum gear. 

If you can afford the Sora groupset, it's worth having.