I'm no expert, but believe that most modern aircraft do allow the pilots some control over the recirculation fans. These do not control cabin pressure or temperature but how much fresh air is used from the packs. This essentially robs the engines of some of the air used to generate thrust, and therefore increases fuel consumption. It can make a significant difference, somewhere between 1-3% if I remember correctly.

Maybe a pilot or engineer can chime in if I'm way off base, but in any case I can't imagine that recirculation fan settings is something that pilots would routinely have to adjust. I remember reading somewhere that on some aircraft there is just a NORMAL and a HIGH setting. At the end of the day there is some merit to the idea of fresh vs dirty air onboard aircraft. I think the cockpit receives no re-circulated air at all, and the people at the back near the outflow valve get to breathe in all the 'dirty' air. Besides, there are other possible sources of air contamination onboard aircraft besides fellow passengers...for those who may not be aware, google 'aircraft toxic fume events' or similar.