I currently use a 2010 MacBook Air as a server with a Western Digital external drive. It replaced a very old Mac Mini, it was a early intel version. The ram was max out at 2 gig's. The Air was my personal computer. The screen is only 11 inches and had become too small for daily use. I upgraded to a larger screen computer, gave the still perfect Mac Mini to my sister and transferred music server duties to the Air. Also the Air has only 2 gigs of ram.
With regard to iTunes music playback, no real listening change. Yet, Screen Sharing and all remote functions improved. Every click is quicker.