If you are having any performance issues, look into tweaking your wireless router config. Maybe change channels if you happen to be on a congested one with other people in an apt complex near you. Also with the new chromecast 2 we will finally see 5ghz support.
You can't abolish buffering on wifi but you only see buffering if you keep seeking, so stop seeking so much. :)
Big question is, whos chromecast is near an ethernet cable? Heck the whole POINT of using a chromecast and videostream is as a wireless hdmi solution. If I was going to add a wire, I would just add an hdmi wire.