I think that having the compressor outside, or in a different room, is a great idea. If I ever get around to building my shop, that's what I'm going to do. Currently, it's in my garage, it doesn't take up any room because it's under my workbench. It's noisy, and for that reason alone, I would move it if I had a place to put it.
I drain my tanks a few times a year. It's amazing how much water gets in there. My compressor is a wheelbarrow style Emglo, so there are two tanks. It also has a wheel to move it around like a wheelbarrow, so it's easy enough to get outside to drain the tanks. It just takes a little time to get it done.
If I had it outside, my biggest fear would be dirt dobbers. They will find a way to plug up every hole that you have. I've had to through away an air line that they plugged up so badly that I just gave up trying to clean it out. I can't imagine what they would do to an outdoor air compressor, but I know they will do something!!!!!