Maybe I've got the wrong end of the stick but never noticed a problem with Wifi for the RPi if only used for control purposes (play, pause, etc).

The processing is negligible and can't see how it has any effect on the music making process whatsoever.
File transfer is a totally different ball game - absolutely pants in my experience and much better direct via ethernet.

That said, I installed IR receivers on mine for general play commands via remote so rarely use the phone/tablet route except for selecting albums.