I to was having the problem using WiFi. I then moved my modem close to my TV so that I could connect it directy with an ethernet cable. No more stopping and starting.
You will never get the same bandwidth using WiFi as you do using a direct cable connection.
That's true. But you don't even need decent bandwith for Netflix shows in HD. Even the company itself recommends at least 5 mbps for HD, so a 10-yr old router should be able to stream to loads of devices simultaneously without any issues whatsoever.
The problem isn't with wifi bandwidth but with some buggy ATV software that for some reason has messed up the wifi.