Readers contributed many good solutions to this challenge. The mundane solution involves using
query-replace-regexp with regular expressions
\(w+\) → (\1)
for 14 keystrokes or, if you’re a bit more clever
w+ → (\&)
for 10. Actually, I have
electric-pair-mode enabled so my counts were 13 and 9 but the 14 and 10 counts work for a stock Emacs.
My best solution was much like those contributed by readers