I expect I would need a compatible bottom bracket too, like the one that this Claris crankset is frequently bought together with, here. The front derailleur is already a Claris, a few months old.
This is on a Jamis Aurora 2000 that I have been riding since 2003. Between my aging and the bigger hills here in San Francisco, where the bike and I moved two years ago, the gearing on the Sora, at 52/42/30, feels a bit too tall anyway. The Claris at 50/39/30 might suit better.
Would this be worth doing? The bike fits me well, I'm fond of it. The stock wheels are aging and the cantilever brakes are squealing, but it's still a fun ride. I'd have this done by the bike shop, I'm no mechanic myself.