I think that if you had access to the dash ducts then it would be an excellent idea to insulate them.
I've been thinking about The Viper's mods as the next thing I would likely do, and the last few posts have really cleared up a lot. We had an unusually hot summer in the northeast this year, and frankly, I left the top on more often than not when it was over 90, because the AC simply can't keep up, what with the huge amounts of hot air coming in over the windshield (though it is better with the windows down). So, last week, we had a cool evening finally, and I thought wow this will be great. Surprisingly, all the hot air that used to come up over the windshield seemed to have gone away, and had to put the heater on, but really did not help as much as I expected. This is just another weird aspect of my car, I guess. I agree that there doesn't seem to be a lot of difference between fan speeds, and I think that whatever gain you achieve from moving the air faster (feels cooler) is lost because the air does not have enough time to be colled before coming out of the vents. Sounds like in this area, removing the plates in the summer, and velcro-ing them back in the winter might be just the ticket. Not sure about whether blocking the ducts/unblocking the ducts should be part of that process. Last question: I expect to remove my dash at some point in the relatively near future, and wondering about whether insulating the vents would be helpful. I remember a much older post that asked about this in relation to the amount of heat on the dash when in direct sunlight. The air is only traveling a short distance there, but I'm thinking every little bit helps?