The idiom stands for constantly strive for improvement.
When I look at 精益求精, I read
Excellence increase seek excellence
But shouldn't it be
Excellence increase seek more excellence
Of course if you added 曾加 then it no longer be four characters long.
Is it a topic comment sentence: As far as excellence goes, it is improvement that seeks it (excellence itself). (?)
Can someone please better explain the arrangement XY求X?
Are there other 成语 of this form?