Does opening the door to the attic have a affect on the AC efficiency in the house? In the hot weather, I keep my 2 garage doors open and the back rear door to get air flow to keep the garage cool in the Arkansas summers. I also have a screen door to the attic which has steps to walk up (unfinished and insulated) and is located in the garage. I use this to ventilate what little air that will get up the steps to the attic which has several attic spinners. In listening to your show I hear you tell people not to create a void in the attic and that house AC will be drawn to it? I am in an all electric house and actually my electric bill has been very reasonable. I use a setback thermostat and cool the house mainly early evening till midnight.
Using an attic fan can have a negative impact on AC costs as the fan will depressurize the attic drawing cooler, conditioned air into that space and out to the environment. It sound's like in your case the attic may be over the garage? If that is the case there is no issue. If the attic is indeed inside living space, then leaving it open will not help your cooling costs.
This said, most of the concerns stem from the use of attic fans and not passive venting which is what you've described. More here about attic fans and air conditioning.
Your right, no fans in attic just whirly's or spinners in the attic. The attic is used for addtional storage with plywood flooring above the garage and the the remaining over the house (same attic) majority has thick blowed in installation. Enjoy your show (a rebroadcast) while walking on Sunday mornings (KARN 102.9, Little Rock). We live in Hot Springs Village, Arkansas.
By the way we use a lot of the products that you guys recommend on you show.