How often do you shut it down? From personal experience, I only shut it down with every update. If I am not using it, it is sleeping, if I am sleeping, my MBA is sleeping as well.
Apple Mobile Computers are not like PC Laptops, since Apple has put an insane amount of optimization on the sleep function. If you sleep your MBA, it will only take around 1 second, or the time it takes you to close the lid. You can sleep the computer for 30 days and still wake up instantly, around 1 second as well. The reason that I emphasize the sleep function, is because there are no mechanical parts on your MBA, thus, the sleep function has much greater benefit from that.
I may not have a solution for your problem, but it has always bugged me to hear people that they completely shut down their machine and treat it as a PC or not know how optimized is the sleep function on Apple Mobile Computers (against the awful sleep function on PC), or they are simply skeptical about the sleep function.
The same principle goes with the iPhone, I've never encounter anyone that shuts it down, if not in use, they are always sleeping, being a smaller device doesn't make any difference.
Anyways, I hope this helps.
