When I am MT/OT healing I like to keep stoicism up before the other wards, so that it's damage is absorbed first. Something like Stoicism->ST->Group, and then cast the ST and Group wards as needed.
I think ward spamming is a bad idea. Not only can you overwrite a crit / super ward with a less powerful ward, but there are things you could be doing other than spamming wards, such as fitting in a debuff or DPSing. I keep track of the time and remaining absorption of all my wards, and if the ward is down I will recast it, but if it is still up I look at two tings:
- How much time is left on the ward (If only a couple seconds remain on the ward then I will recast it).
- How much absorbtion is left on the ward (If my ward has not been damaged then I will not recast it).
I use profit UI and keep my maintained window right next to my hotbars and group window so that I can see exactly how much time and absorption my wards have left.