Any semantic difference between the two following sentences?
See if there isn't any room for improvement.
See if there is any room for improvement.
Native speaker - I think these are basically equivalent. In both cases, the imperative is to check whether room for improvement exists, so the activity is the same.
There's a slight difference of tone. I would normally use "see if there isn't" in cases where I think there is room for improvement but I'm speaking to someone who disagrees; the implication is that I want them to conduct a more thorough search. But "see if there is" is also correct in that case.
I think you're good either way.