I got the same issue here, and i wonder if there is already a solution for this problem. (because the thread is from 2009). I'm using inventor 2013.
You could set Tools>Application Options>General tab to a real small value on Annotation Scale to make them less visible, but this will also make sketch dimension annotations very small.
i also get into the same issue
is there something done meanwhile?
I just found that by going to properties for the sketch into which you've imported the ACAD drawing, you can change lineweight and all the points become far less prominent.