Capacitor voltage rating vs. sound quality

In my experience there is no sonic benefit. The voltage rating is designed to protect the capacitor. Generally, if you increase the voltage and retain the same capacitance, the capacitor will have a larger form factor, but the sonics should be equivalent to the same brand/model capacitor with a lower voltage rating. 

Film caps get big quick, so don’t go too high over the voltage rating you need. 

Size is usually a much bigger deal. Some film caps are huge per uF, and even bigger with high voltage types.  Also, depending on the film types it may be that only high voltages are available in very low values.

Point is, equal or exceed original voltage values, but you may find yourself forced to use one or the other based on the application. 

Lastly, big V is more expensive than small V.

I'll bet that if this were really studied people would have another thing to talk about.