Well, the little vamp just before Clara begins to sing in Say it Somehow is extremely common, so that probably has something to do with it, but I'd definitely say Guettel was influenced by Sondheim. I mean, it's pretty much impossible to write musicals these days and not have SOME Sondheim influence (unless you write in the ALW school).
But yes, the first two bars in the printed version of Say It Somehow are extremely similar to the bars leading into the words "Nothing's gonna harm you", but also bear a relation to "What I Did For Love". I think it's just a common pattern.
"I could use a little...
Miracle."
~SWIWS