I'm actually researching new phones and plans, too. My Moto G still works fairly well, but the 8GB of storage and the lack of a Micro SD slot means I'm constantly out of space for app updates. I'm using my phone more heavily than I used to, and the battery doesn't always make it through a day anymore. My plan with Republic Wireless was great for cheapness, but with it constantly trying to connect to WiFi, its supposed strength becomes its weakness - when transiting between free public WiFi and 3G-only areas, there can be major delays for texts and phone calls. It's even worse in areas where there are many free access points, such as in a mall (where I work). One other minor frustration is that many services won't recognize my phone as being a legitimate number, so I can't use it for two-factor authentication with them.
So, while I won't have as nice of a bill (<$15-25/month), $30-$35 without the current frustrations would be acceptable.