Should I get rid of my iPhone for a non smartphone to save money?

I have an iPhone 4 with family plan with my wife. She has Droid X. We are thinking of downgrading. It will be $110 a month instead of $170 a month. I use e-mail often and don't really need wi-fi. I heard the ENV Touch was a great non-smartphone. Will it still be fast? Will I be happy with it? Is it worth it? I will also be getting $328 in the form of a check for my iPhone 4. Please help, any advice is appreciated.