Is there any advantage to USB 3.0 on an external DVD writer?

Short answer : No, unless you are using a high-quality BluRay writer.

A DVD writer at 8x means a max theoretical speed of 8 X 4.5 MB/s which equates to 36 MB/s. USB2 has a real world speed of around 35 to 40 MB/s, therefore is good enough for these drives.

However, for BluRay writers at 12x or 16x, this means a theoretical speed of 54 or 72 MB/s, which is more than USB 2 can handle.

Another difference is power usage, where USB2 can do up to 500 mA, while USB3 can do up to 900 mA. USB2 power may be a limiting consideration when buying a DVD writer.

But I'm not sure that the difference in real world speed in using a 12x/16x drive via USB2 vs USB3 is worth the price difference, especially if you are not planning on using BluRay.