Regarding your second suggestion, we could also use . instead of &, as that's what Perl and PHP do - feels a little more natural to me. But . might cause me a little mental friction in differentiating between the different uses of . in (. "a" "b") and (do (= a '(1 2)) a.0).
To be honest, I'm still not crazy about the idea simply because I don't need the speed boost and + doesn't seem to cause me to use extra mental cycles when reading my code. I'd be open to it though if the community really wanted it that way.
We could vote and also ask PG what he thinks and then make a decision.