A different implementation approach, could be that the search is performed as you type an answer. (in the same way that "Related questions" are highlighted as you write a question).
This would only occur on questions with more than 'x' 1 answers.
As to the 'value' of this feature:
I agree that there are few questions to which this pertains -- but for those questions the problem is chronic, and because those questions are 'frequently answered' they appear on the front page often.
So to determine the 'importance' of the feature we'd need to look not just at the number of questions if affects, but the total number of answers it would help with (this is a much bigger number)
1. 'x' would be a number at least big enough to cause answers to spill onto a second page.