Claris vs Sora shifters I'm upgrading my road touring bike, currently with a 3x8 drivetrain and bar-end friction shifters. I'm going for integrated brake/shift levers, and wondering about the difference between the Claris ST-2400 and Sora ST-3500 STI shifters.

I already know that the Claris is 3x8 and the Sora 3x9. Upgrading to a 9-speed cassette and chain should be no problem (chain rings are already 9-speed compatible). I'd choose the same cassette range for either, and I don't think having the extra intermediate gear would matter much to me.

My question is: are the Sora shifters better (in terms of materials, reliability, smoothness, accuracy, or whatever) than the Claris? It's a 50-ish dollar difference, so that's not that big a deal. Anything else I might've missed? I'm not really interested in going to a 10 (or more) speed rear, so the higher end mechanisms are out.
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.