yes you answered my question and then some.     we too struggle to know what to do for sure when dealing with the aphid.

last Monday I was out in a late planted soybean field of mine.  was out there for three hours pulling weeds and scouting, seen very few aphids. Wednesday my agronomist was driving by and he decided to stop and do some scouting, the first plant he pulled had 300 aphids on it.  what the heck, he said he scouted around and it wasn't too hard to find big aphid populations on other plants.