My expectation has always been that life is pretty widespread
in the Universe, and that intelligent life is not uncommon, so
something like finding that arsenic can replace phosphorus in
the DNA of some bacteria isn't much more than "Well, duh!"
for me. It's the sort of thing I'd expect. When I took biology
in high school I wrote a paper on non-carbon based alien life.
That was in early 1969. My paper wasn't very good, but I tried
to discuss some of the possibilities. From what I've learned
since, I have to agree that carbon-based life seems far more
likely, and is therefore probably more common.
A friend created her own major in college. She got her degree
in exobiology. I'll have to ask her to be sure, but I think that
was in the early 1970's.
-- Jeff, in Minneapolis