I don't think its necessary to alternate with one bottle of "plain water" and another with a mix of some kind. If the mix is done with a good product, then it doesn't make much sense to use an alternating bottle of plain water.

Riders who have been riding for years will know or should know what conditions dictate how much and what to eat and drink. Taking a break on long rides is actually good for the body. I figure its not always a demanding group ride, and stopping to pee or drink or eat is ok. Your body will approve. But your ego might get in the way.