Certainly - the points system is there to encourage people to make that extra effort to capture squares we don't have photos for yet, but we welcome additional images, perhaps showing a different subject, or a different time of year. You could be gaining yourself a personal point too.
Everyone sees things differently - feel free to give us your take on any square. Some squares have been done in considerable detail, helping to more fully document and add depth to a square. In particular, watch out for things others may have missed - the coverage maps can help with this.
Long term, multiple images taken at different times, even of the same subject, help to document change or the lack thereof.