i also leave mine on 3G most of the time. at home and work i have wi-fi. all my friend's places have wi-fi. in the car when i'm driving, there's no need for 4G since I can't really use the phone much and google maps works fine on 3G. Music streaming is fine as well with 3G. so really i just turn on 4G when i need it. wish there was a 4G toggle widget that worked. i have "LTE switcher" which is good enough for now i guess.
Also you guys should check out "y5 battery saver". it turns on your wi-fi automatically in known areas by remembering the voice cell networks around. works pretty good for me.
few issues which aren't too bad:
1. when you happen to be connected to a different voice network than what was "remembered" by the app, you'll have to manually turn on your wi-fi.
2. if you are in a big city and go down the street, Y5 will keep your wi-fi on since it thinks you are in the area.
3. in order to turn off your wi-fi in a known wi-fi area like in scenario 2, you have to turn off Y5. otherwise it will keep turning your wi-fi back on when you turn it off.