We are getting away from what the original question is. I have not seen an air drill with a clutch only because they wouldn't be of much use. Air tools are specific in use not like electric which tries to cover many uses. So hence why they don't have a clutch because there are air impact drivers and air screwdrivers. I do agree that if air powered was better that you would see many more contractors using them (except nailers).
The question you have to ask yourself, is "Am I going to use it after the job is done?". If you don't have much other use for it beyond the scope of the deck, I wouldn't go that route. Then think about compressor capacity. Is your compressor capable of the scfm needed for the drill? Since it would be in use for longer durations, you need a compressor that is at least a 30 gallon or higher and able to deliver at least 8-9 scfm at 90 psi. Then if your compressor is smaller, it constantly has to play catch up and then it is running nonstop. It would be about the same as if you left your table saw running the entire time you were building the deck. Not very good on the electric bill.
I myself would go the cordless impact driver way since you said it is about 140 square feet. You said that your drill is about 7 years old. I would look at a drill/impact driver kit and keep your old one for the times you could use 2 drills. I doubt that you would find an impact driver kit that you could use the batteries on your old drill.
I have an air drill, It is nice for drilling wood because of the low torque and high rpm, but I would not try to drive screws with it.
Allen