I am no expert but I would say it depends on a) what the weather is like during the reunion b) how short the dress is and c) if you are comfortable with your leg tone or not! If its going to be hot or if you legs are toned and tanned, I would say go for the no hose (also if its a day event)
If its going to be in the evening or if your dress is shorter than an inch above the knee, I would think hose would be nice. Maybe just skin toned ones....