I think subconsciously I'd feel "safer" for whatever reason.. Having a cap on it? But functionality wise, I think it's better without one.
But to be honest... Mine never gets dirty, I don't have any problems with it all... Just don't have to unscrew anything to fuel up... And no stupid lid flapping around against my paint , because of a poor fuel cap latch design. Used to drive me up the wall, with my last car... The cap would never sit on the latch that it was supposed to be on, because the cheap plastic connecting piece... had too much tension, and it would always pop off, or just fall off because the hook wasnt big enough. (Thanks GM)
Anyway, my verdict on the capless setup.... No harm no foul. I have no desire to fork up any money to fix what aint broke.
That said, if prices keep climbing and my neighborhood jumps in on the stealing fuel from your neighbor thing... I may be singing a different tune.