Just in case someone misreads this, add the vinegar as the softener, so it's not in the first load that contains the detergent. The detergent is a base, and relies upon that fact to get rid of some of the stains, and vinegar as an acid will neutralize that. Vinegar is meant to be in the rinse cycle when washing laundry, where it can help get rid of any extra detergent by neutralizing it and do any other magic it does.

Also, though I don't usually encounter them often, do note that vinegar can wash away zinc and silver oxides used for some sterile clothing, and can supposedly damage lyocell.

But overall I second these suggestions. Most times the amounts listed for detergent are far too big, and you can often get by with less.

I have a rule where undies are a one and done, tshirts are twice then in the wash, and pants are until they look dirty. I don't do the same for shirts as i do pants because of armpits. If only i had pit undies... hmmm....