If it's raining do still visit the peak however do it at night. The lights coupled with the rain looks beautiful IMO as long as your ok with getting wet. During the day the cloud cover / fog makes it pointless. Try exploring some buildings and malls. You can go up the Bank Of China tower which is pretty neat as well as a few other notable buildings in HK. If your into meeting new people or watching sports then head to Soho and visit the pubs.