Well Tripoto asks what you did on Day 1 and that's exactly is the reason number 1 to visit Yercaud - It's a Perfect 1 day trip (Well I am assuming that Bangalore is the only place from where people will throng to this nice little place.
2 . ROADS......
NH 7 is sexy. The best part of this route is that you will be greeted with amazing scenery all the way through from Bangalore to Salem.
From Salem the roads goes uphill for 30 kms till Yercaud. See it to believe it (few pics below)
3. One Cheeky Rascal - I am sure all of you have read it but someone became innovative and open a fun place called Sweet Rascal. After your feet is sore with all the sight seeing points (which to me is average exp) and your stomach is rumbling - head out to this place. It's worth visiting