Hey Bill,
ATC spindles were invented for the purpose. I think the addition of compressed air (what you need for a real ATC spindle) is something many people already have in their workshop and would be less effort than adding this.
One thing to consider is dust and debris, that can easily be around and get inside your ER collet, where it will lead to runout problems (which not only will reduce your milling accuracy but also can damage your spindle bearings). With a real ATC spindle, you have sealing air inside the spindle which prevents dust entering the tool holder taper completely.