I have been on both sides of this one. As a student, I had a solid step I score (230"s), but chose to take step II early to get it out of the way. You have the option of reporting the score or not on ERAS, so I watied to report until I got my score back. When the score was higher than my step I, I reported it. Did it help me with interviews? I can't say for sure, but I had three PDs comment that they were impressed that I took it early, so I know they looked at it.
As a resident, I look to see if people have taken step II when screening the applications, as do some of the other residents in my program. If you improve your score, it will definitely make up for an average step I score. Some programs may screen only by step I, but I don't think that is standard.
I look at it this way. You cannot hurt yourself by taking step II early. Choose not to report the score until you receive your results. If you improve your step I score, submit them. It may help you with some programs and you are no worse off if it doesn't. If you do poorly, choose not to submit and you are no worse off.